Lighting device and display device

ABSTRACT

A backlight unit includes LEDs, a light guide plate, a prism sheet, exiting light reflecting portions, prisms, concave lenticular lenses, and flat portions. The concave lenticular lenses are configured such that an occupancy rate of concave cylindrical lenses with respect to the second direction is higher in an area closer to a light entering surface with respect to the first direction and the occupancy rate is lower in an area farther from the light entering surface. The flat portions are formed adjacent to the concave cylindrical lenses with respect to the second direction such that an occupancy rate of flat portions with respect to the second direction is lower in an area closer to a light entering surface with respect to the first direction and the occupancy rate of the flat portions with respect to the second direction is higher in an area farther from the light entering surface.

TECHNICAL FIELD

The present invention relates to a lighting device and a display device.

BACKGROUND ART

Display components in image display devices, such as television devices,are now shifting from conventional cathode-ray tube displays to thindisplay panels, such as liquid crystal panels and plasma display panels.With the thin display panels, the thicknesses of the image displaydevices can be reduced. Liquid crystal panels included in the liquidcrystal display devices do not emit light, and thus backlight devicesare required as separate lighting devices. The backlight devices aregenerally classified into direct-type and edge-light-type according tomechanisms. An edge-light-type backlight device includes a light guideplate for guiding light from a light source and an optical member forconverting the light from the light guide plate to even planar lightwith optical properties and for supplying the light to a liquid crystalpanel. An example of such a device is disclosed in Patent Document 1.Patent Document 1 discloses a configuration that includes multipleridged lenses on a light exiting surface of a light guide plate suchthat the light guide plate has light collecting properties to improvebrightness without a prism sheet.

RELATED ART DOCUMENT

Patent Document

Patent Document 1: Japanese unexamined patent application publicationNo. 2005-71610

Problem to be Solved by the Invention

Although a technology disclosed in Patent Document 1 using the ridgedlenses on the light exiting surface of the light guide plate may improvea frontward brightness of exiting light, uneven brightness is morelikely to occur. Point light sources are arranged at intervals along alongitudinal direction of a light entering surface of the light guideplate in Patent Document 1. In an area of the light guide plate closerto the light entering surface, bright spots and dark spots tend toappear along an arrangement direction of the point light sources, thatis, uneven brightness tends to occur in light exiting from the lightexiting surface. With the ridged lenses described above, brightness ofthe bright spots is further increased and thus the uneven brightness inthe area close to the light entering surface is more likely to occur.

DISCLOSURE OF THE PRESENT INVENTION

The present invention was made in view of the foregoing circumstances.An object is to reduce uneven brightness.

Means for Solving the Problem

A lighting device according to the present invention includes a lightsource, a light guide plate, alight exiting-side anisotropic lightcollecting portion, an exiting light reflecting portion, a prismportion, a lenticular lens portion, and flat portions. The light guideplate has a rectangular plate shape. The light guide plate includesperipheral end surfaces opposite from teach other and plate surface. Atleast one of the peripheral end surfaces is configured as a lightentering surface through which light emitted by the light source enters.One of the plate surfaces is configured as a light exiting surfacethrough which the light exits. The other one of the plate surfaces isdefined as an opposite surface. The light exiting-side anisotropic lightcollecting portion formed on a light exiting side. The lightexiting-side anisotropic light collecting portion includes lightexiting-side unit light collectors that extend along a first directionthat is parallel to peripheral end surfaces of the light guide plate notincluding the light entering surface. The unit light collectors arearranged parallel to one another along a second direction parallel tothe peripheral end surfaces including the light entering surface. Theexiting light reflecting portion is formed on one of a light exitingsurface side and an opposite plate surface side of the light guide platefor reflecting light traveling through the light guide plate such thatthe light exits from the light exiting surface. The exiting lightreflecting portion includes unit reflectors that extend along the seconddirection and are arranged at intervals along the first direction. Theprism portion is formed on one of the light exiting surface side and theopposite plate surface side of the light guide plate. The prism portionincludes unit prisms that extend along the first direction and arearranged along the second direction. The lenticular lens portion isformed on the other one of the light exiting surface and the oppositeplate surface of the light guide plate. The lenticular lens portionincludes cylindrical lenses that extend along the first direction andare arranged along the second direction such that an occupancy rate ofthe cylindrical lenses with respect to the second direction is higher inan area closer to the light entering surface and lower in an areafarther from the light entering surface. Flat portions are formed on theother one of the light exiting surface and the opposite plate surface ofthe light guide plate. The flat portions are flat along the firstdirection and the second direction. The flat portions are arrangedadjacent to the cylindrical lenses with respect to the second directionsuch that an occupancy rate of the flat portions with respect to thesecond direction is lower in the area closer to the light enteringsurface and higher in the area farther from the light entering surface.

According to the configuration, the light emitted by the light sourceenters the light guide plate through the light entering surface andtravels through the light guide plate. During the transmission, thelight is reflected by the exiting light reflecting portion. The unitreflectors of the exiting light reflecting portion extending along thesecond direction are arranged at intervals along the first direction.Therefore, the light traveling through the light guide plate along thefirst direction is reflected and directed to the light exiting surfaceto exit through the light exiting surface. Anisotropic light collectingeffects are added to at least some rays of light exiting from the lightexiting surface by the prism portion and the lenticular lens portion.The prism portion and the lenticular lens portion include unit prismsand the cylindrical lenses, respectively. The prisms and the cylindricallenses extend along the first direction. The prisms and the cylindricallenses are arranged along the second direction. Light collecting effectsare selectively added to at least some rays of light exiting from thelight exiting surface by at least one of the unit prisms and thecylindrical lenses with respect to the second direction.

Rays of light traveling through the light guide plate along the firstdirection without being reflected by the exiting light reflectingportion are totally reflected by the prism portion and the lenticularlens portion. As a result, the light travels through the light guideplate while diffusing with respect to the second direction. Because thelenticular lens portion includes the cylindrical lenses, the rays oflight totally reflected by the cylindrical lenses are more likely to bescattered to a wider area with respect to the second direction.

The anisotropic light collecting effects are added to the light exitingfrom the light exiting surface of the light guide plate by the lightexiting-side anisotropic light collecting portion on the light exitingside relative to the light guide plate. Because the light exiting-sideanisotropic light collecting portion includes the light exiting-sideunit light collectors that extend along the first direction and arearranged along the second direction, light collecting effects areelectively added to rays of light exiting from the light exiting-sideunit light collectors with respect to the second direction, whichcorresponds with an arrangement direction of the light exiting-side unitlight collectors. Although the cylindrical lenses of the lenticular lensportion add the anisotropic light collecting effects to the rays oflight reflected by the exiting light reflecting portion as describedearlier, the rays of light to which the anisotropic light collectingeffects are added are less likely to be collected with respect to thesecond direction at the light exiting-side anisotropic light collectingportion and more likely to be scattered with respect to the seconddirection. The flat portions adjacent to the cylindrical lenses withrespect to the second direction are less likely to add specific opticaleffects to the rays of light reflected by the exiting light reflectingportion. Therefore, the anisotropic light collecting effects aredominantly added to the rays of light directed to the light exiting-sideanisotropic light collecting portion via the flat portions by the prismportion. In the light exiting-side anisotropic light collecting portion,the light collecting effects are more likely to be added with respect tothe second direction. As the occupancy rate of the cylindrical lenses ofthe lenticular lens portion with respect to the second direction is sethigher and the occupancy rate of the flat portions with respect to thesecond direction is set lower, uneven brightness of light exiting fromthe light exiting-side anisotropic light collecting portion with respectto the second direction is more likely to be reduced but brightness ismore likely to be reduced. As the occupancy rate of the flat portionswith respect to the second direction is set higher and the occupancyrate of the cylindrical lenses with respect to the second direction isset lower, the uneven brightness of the light exiting from the lightexiting-side anisotropic light collecting portion is less likely to bereduced but the brightness is more likely to be improved.

As described earlier, in the area close to the light entering surfacewith respect to the first direction, the occupancy late of thecylindrical lenses of the lenticular lens portion with respect to thesecond direction is higher and the occupancy rate of the flat portionswith respect to the second direction is lower. In the area farther fromthe light entering surface with respect to the first direction, theoccupancy rate of the cylindrical lenses with respect to the seconddirection is lower and the occupancy rate of the flat portions withrespect to the second direction is higher. With the cylindrical lensesof the lenticular lens portion having the higher occupancy rate, in thearea close to the light entering surface in which the uneven brightnessdue to the light source may occur, the uneven brightness is less likelyto occur in the light exiting from the light exiting-side anisotropiclight collecting portion with respect to the second direction. With theflat portions having the higher occupancy rate, in the area farther fromthe light entering surface with respect to the first direction in whichthe uneven brightness due to the light source is less likely to occur,the brightness of the light exiting from the light exiting-sideanisotropic light collecting portion is increased. According to theconfiguration, the uneven brightness in the light exiting from the lightexiting-side anisotropic light collecting portion is reduced and thebrightness is improved.

Preferable embodiments of the present invention may include thefollowing configurations.

(1) The exiting light reflecting portion and the prism portion may beformed on the opposite plate surface side of the light guide plate. Thelenticular lens portion may be formed on the light exiting surface sideof the light guide plate. According to the configuration, at least someof light rays reflected by the unit reflectors of the exiting lightreflecting portion on the opposite plate surface side of the light guideplate are directed to the light exiting surface while the anisotropiclight collecting effects are added by the prism portion and exit fromthe light exiting surface while the anisotropic light collecting effectsare added by the lenticular lens portion formed on the light exitingsurface. In comparison to a configuration in which the exiting lightreflecting portions is formed on the light exiting surface side, lightpaths starting from where the light rays are reflected by the exitinglight reflecting portion and ending where the light rays exit throughthe light exiting surface is simple and a loss of light is less likelyto occur. Therefore, a reduction in brightness is less likely to occur.

(2) Each of the unit prisms of the prism portion may have a vertex anglein a range from 90° to 100°. According to the configuration, incomparison to a configuration in which the occupancy rate of thecylindrical lenses with respect to the second direction is constant, thebrightness of the light exiting from the light exiting surface can besufficiently improved.

(3) Each of the unit prisms of the prism portion may have a vertex angleof 100°. According to the configuration, in comparison to theconfiguration in which the occupancy rate of the cylindrical lenses withrespect to the second direction is constant, the brightness of the lightexiting from the light exiting surface can be improved at a maximum.

(4) Each of the unit prisms of the prism portion may have a vertex anglein a range from 120° to 160°. According to the configuration, incomparison to the configuration in which the occupancy rate of thecylindrical lenses with respect to the second direction is constant, thebrightness of the light exiting from the light exiting surface can besufficiently improved.

(5) Each of the unit prism of the prism portion may have a vertex anglein a range from 133° to 140°. According to the configuration, incomparison to the configuration in which the occupancy rate of thecylindrical lenses with respect to the second direction is constant, thebrightness of the light exiting from the light exiting surface can befurther improved.

(6) The lighting device may further include a reflecting member thatincludes a reflecting surface for reflecting light. The reflectingmember may be disposed opposite the opposite plate surface of the lightguide plate. The exiting light reflecting portion and the prism portionmay be formed on the light exiting surface side of the light guideplate. The lenticular lens portion may be formed on the opposite platesurface side of the light guide plate. According to the configuration,some of the light rays reflected by the unit reflectors of the exitinglight reflecting portion on the light exiting side of the light guideplate are directed to the opposite plate surface and exit with theanisotropic light collecting effects added by the lenticular lensportion. The exiting light rays are reflected by the reflecting memberand directed to the light exiting surface after entering through theopposite plate surface. The light rays exit through the light exitingsurface with the anisotropic light collecting effects added by the prismportion. Namely, light paths starting from where the light rays arereflected by the exiting light reflecting portion and ending where thelight lays exit through the light exiting surface are complicated. Eachof the light rays receives refraction effects at least twice whentraveling from the opposite plate side to the reflecting member and whentraveling from the reflecting member side to the opposite plate surface.The light rays reflected by the exiting light reflecting portion and towhich the anisotropic light collecting effects are not added by theprism portion are less likely to be scattered with respect to the seconddirection due to the refraction effects. Therefore, the light rays areproperly mixed with respect to the second direction and the unevenbrightness is less likely to occur in the light exiting from the lightexiting surface with respect to the second direction.

(7) Each of the unit prisms of the prism portion may have a vertex anglein a range from 135° to 155°. According to the configuration, incomparison to the configuration in which the occupancy rate of thecylindrical lenses with respect to the second direction is constant, thebrightness of the light exiting from the light exiting surface can besufficiently improved.

(8) Each of the unit prisms of the prism portion may have a vertex angleof 150°. According to the configuration, in comparison to theconfiguration in which the occupancy rate of the cylindrical lenses withrespect to the second direction is constant, the brightness of the lightexiting from the light exiting surface can be improved at a maximum.

(9) Each of the unit prisms of the prism portion may have a vertex angleof 110°. According to the configuration, in comparison to theconfiguration in which the occupancy rate of the cylindrical lenses withrespect to the second direction is constant, the brightness of the lightexiting from the light exiting surface can be sufficiently improved.

(10) Each of the cylindrical lenses of the lenticular lens portion mayhave a concave shape. According to the configuration, in comparison tothe configuration in which each of the cylindrical lenses has a convexshape, light rays traveling through the light guide plate are morelikely to enter a curved interface of the cylindrical lens with an angleof incidence larger than a critical angle. Therefore, the light rays areless likely to exit from the interface. The light rays traveling throughthe light guide plate are more likely to be totally reflected and to bescattered with respect to the second direction. Therefore, unevenbrightness is less likely to occur with respect to the second direction.

(11) Each of the cylindrical lenses of the lenticular lens portion mayhave a convex shape. According to the configuration, in comparison tothe configuration in which each of the cylindrical lenses has a concaveshape, light rays traveling through the light guide plate are morelikely to enter a curved interface of the cylindrical lens with an angleof incidence smaller than the critical angle. Therefore, the light raysare more likely to exit from the interface.

(12) The exiting light reflecting portion and the prism portion may beformed on the opposite plate surface side of the light guide plate. Thelenticular lens portion may be formed on the light exiting surface sideof the light guide plate. The cylindrical lenses of the lenticular lensportion may include a first cylindrical lens having a smaller height anda second cylindrical lens having a larger height. A clearance may beprovided between the first cylindrical lens and the light exiting-sideanisotropic light collecting portion. With the clearance between thefirst cylindrical lens of the cylindrical lenses and the lightexiting-side anisotropic light collecting portion, the lightexiting-side anisotropic light collecting portion is less likely to bein close contact with the lenticular lens portion. According to theconfiguration, uneven brightness of light exiting from the lightingdevice can be reduced.

(13) The lenticular lent portion and the flat portions may be formedsuch that the occupancy rate of the cylindrical lenses with respect tothe second direction gradually and continuously decreases as a distancefrom the light entering surface with respect to the first directionincreases and occupancy rate of the flat portions with respect to thesecond direction gradually and continuously increases as the distancefrom the light entering surface with respect to the first directionincreases. According to the configuration, in comparison to theconfiguration in which the occupancy rate of the cylindrical lenses ofthe lenticular lens portion with respect to the second direction and theoccupancy rate of the flat portions with respect to the second directionare altered stepwise, the uneven brightness is more properly reduced.Furthermore, this configuration is more preferable for improving thebrightness.

(14) The unit reflectors of the exiting light reflecting portion mayinclude segment unit reflectors arranged at intervals with respect tothe second direction. An amount of light reflected by the unitreflectors tend to be proportional to a surface area of the unitreflectors. To achieve a necessary amount of reflected light, a surfacearea corresponding to the necessary amount of reflected light isrequired. If the unit reflectors are formed to extend for an entirelength of the light guide plate with respect to the second direction,dimensions of the unit reflectors in a direction normal to the platesurface of the light guide plate cannot be increased more than specificdimensions to achieve the surface area of the unit reflectors. With theunit reflectors including the segment unit reflectors arranged atintervals with respect to the second direction, the dimensions of theunit reflectors in the direction normal to the plate surface of thelight guide plate can be increased to achieve the surface area of theunit reflectors. If the light guide plate is prepared by molding and theexiting light reflecting portion is integrally formed with one of thelight exiting surface and the opposite plate surface of the light guideplate, the segment unit reflectors of the unit reflectors on one of thelight exiting surface and the opposite plate surface can be more easilyformed in designed shapes. Therefore, the exiting light reflectingportion can properly deliver optical performances.

If the unit reflectors are formed to extend for the entire length of thelight guide plate with respect to the second direction, the number ofthe unit reflectors with respect to the first direction may be reducedto adjust the total area that is calculated by adding up surface areasof the unit reflectors. According to the configuration, unevenbrightness may occur because the intervals of the unit reflectorsarranged in the first direction increase. With the unit reflectorsincluding the segment unit reflectors arranged at intervals with respectto the second direction, it is not necessary to alter the number and theintervals of the unit reflectors with respect to the first direction.Therefore, uneven brightness is less likely to occur in light exitingfrom the lighting device.

(15) The unit reflectors of the exiting light reflecting portion areformed by cutting portions of the unit prisms of the prism portion onthe vertex side to open along the second direction. If the unitreflectors do not open along the second direction but have side surfacesalong the first direction, light rays may be refracted at or reflectedby the side surfaces along the first direction. Namely, the prismportion may not deliver a proper level of light collecting performance.With the exiting light reflecting portion that includes the unitreflectors that are formed by cutting the portions of the unit prisms onthe vertex side to open along the second direction, the prism portioncan properly deliver the light collecting performances. According to theconfiguration, the brightness of the light exiting from the lightingdevice can be further improved.

Next, to solve the problem described earlier, a display device accordingto the present invention includes the lighting device described aboveand a display panel for display images using light from the lightingdevice.

According to the display device having such a configuration, images aredisplayed with high display quality because uneven brightness is lesslikely to occur in light exiting from the lighting device and highbrightness is provided.

Advantageous Effect of the Invention

According to the present invention, the uneven brightness is less likelyto occur.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view illustrating a generalconfiguration of a liquid crystal display device according to a firstembodiment of the present invention.

FIG. 2 is an exploded perspective view of illustrating a generalconfiguration of a backlight unit in the liquid crystal device.

FIG. 3 is a cross-sectional view of the liquid crystal display devicealong a long-side direction thereof (a first direction, the X-axisdirection) illustrating a cross-sectional configuration.

FIG. 4 is a cross-sectional view of the liquid crystal display devicealong a short-side direction thereof (a second direction, the Y-axisdirection) illustrating a cross-sectional configuration.

FIG. 5 is a magnified cross-sectional view of an LED and therearoundillustrated in FIG. 3.

FIG. 6 is a plan view of a light guide plate.

FIG. 7 is a bottom view of the light guide plate.

FIG. 8 is a magnified plan view illustrating an end portion of the lightguide plate on a light entering surface side and an end portion of thelight guide plate on an opposite end surface side.

FIG. 9 is a cross-sectional view along line A-A in FIG. 6.

FIG. 10 is a cross-sectional view along line B-B in FIG. 6.

FIG. 11 is a cross-sectional view along line C-C in FIG. 6.

FIG. 12 is a cross-sectional view along line D-D in FIG. 6.

FIG. 13 is a graph illustrating relationships between angles ofincidence of light entering a prism sheet and angles of emergence oflight exiting from the prism sheet.

FIG. 14 is a graph illustrating relationships between vertices of unitprisms of the light guide plate and relative brightness levels of lightexiting from the prism sheet in comparative experiment 1.

FIG. 15 is a graph illustrating brightness angle distributions of lightexiting from the prism sheets after exiting from the light guide platesand traveling through the prism sheets of comparative examples 1 and 2with respect to the second direction in comparative experiment 2.

FIG. 16 is a table including pictures of the light guide plates ofcomparative examples 1 and 2 and embodiment 1 taken from the lightexiting surface side and illustrating results of determination aboutuneven brightness in comparative experiment 3.

FIG. 17 is a graph illustrating brightness angle distributions of lightexiting from the prism sheets after exiting from portions of the lightguide plates closer to the light entering surfaces with respect to thefirst direction and traveling through the prism sheets of comparativeexample 2 and embodiment 1 with respect to the second direction incomparative experiment 4.

FIG. 18 is a graph illustrating brightness angle distributions of lightexiting from the prism sheets after exiting from middle portions of thelight guide plates with respect to the first direction and travelingthrough the prism sheets of comparative example 2 and embodiment 1 withrespect to the second direction in comparative experiment 4.

FIG. 19 is a graph illustrating brightness angle distributions of lightexiting from the prism sheets after exiting from portions of the lightguide plates closer to the opposite end surfaces with respect to thefirst direction and traveling through the prism sheets of comparativeexample 2 and embodiment 1 with respect to the second direction incomparative experiment 4.

FIG. 20 is a graph illustrating heights of unit reflectors of exitinglight reflecting portions of the light guide plates according tocomparative example 3 and embodiment 1 in comparative experiment 5.

FIG. 21 is a table illustrating the heights of the unit reflectors andshape reproducibility at first to fifth positions on the light guideplates according to comparative example 3 and embodiment 1 incomparative experiment 5.

FIG. 22 is a cross-sectional view along line A-A in FIG. 22.

FIG. 23 is a cross-sectional view along line A-A in FIG. 22.

FIG. 24 is a cross-sectional view along line B-B in FIG. 22.

FIG. 25 is a cross-sectional view along line C-C in FIG. 22.

FIG. 26 is a cross-sectional view along line D-D in FIG. 22.

FIG. 27 is a graph illustrating brightness angle distributions of lightexiting from the prism sheets after exiting from the light guide platesand traveling through the prism sheets of comparative examples 4 and 5with respect to the second direction in comparative experiment 6.

FIG. 28 is a graph illustrating relationships between vertices of unitprisms of the light guide plate and relative brightness levels of lightexiting from the prism sheet in comparative experiment 7.

FIG. 29 is a graph illustrating brightness angle distributions of lightexiting from the prism sheets after exiting from portions of the lightguide plates closer to the light entering surfaces with respect to thefirst direction and traveling through the prism sheets of comparativeexample 5 and embodiment 2 with respect to the second direction incomparative experiment 8.

FIG. 30 is a graph illustrating brightness angle distributions of lightexiting from the prism sheets after exiting from middle portions of thelight guide plates with respect to the first direction and travelingthrough the prism sheets of comparative example 5 and embodiment 2 withrespect to the second direction in comparative experiment 8.

FIG. 31 is a graph illustrating brightness angle distributions of lightexiting from the prism sheets after exiting from portions of the lightguide plates closer to the opposite end surfaces with respect to thefirst direction and traveling through the prism sheets of comparativeexample 5 and embodiment 2 with respect to the second direction incomparative experiment 8.

FIG. 32 is a cross-sectional view illustrating a cross-sectionalconfiguration of a light guide plate cut at a position closer to a lightentering surface with respect to the first direction along the seconddirection according to a third embodiment of the present invention.

FIG. 33 is a cross-sectional view illustrating a cross-sectionalconfiguration of the light guide plate cut at a position in the middlewith respect to the first direction along the second direction.

FIG. 34 is a cross-sectional view illustrating a cross-sectionalconfiguration of the light guide plate cut at a position closer to anopposite end surface with respect to the first direction along thesecond direction.

FIG. 35 is a cross-sectional view illustrating cross-sectionalconfigurations of a light guide plate, a reflection sheet, and a prismsheet cut along the second direction according to a fourth embodiment ofthe present invention.

FIG. 36 is a cross-sectional view illustrating a cross-sectionalconfiguration of a light guide plate cut at a position closer to a lightentering surface with respect to the first direction along the seconddirection according to a fifth embodiment of the present invention.

FIG. 37 is a cross-sectional view illustrating a cross-sectionalconfiguration of the light guide plate cut at a position in the middlewith respect to the first direction along the second direction.

FIG. 38 is a cross-sectional view illustrating a cross-sectionalconfiguration of the light guide plate cut at a position closer to anopposite end surface with respect to the first direction along thesecond direction.

FIG. 39 is a plan view of a light guide plate according to a sixthembodiment of the present invention.

FIG. 40 is a plan view of a light guide plate according to a seventhembodiment of the present invention.

FIG. 41 is a plan view of a light guide plate according to an eighthembodiment of the present invention.

FIG. 42 is a plan view of a light guide plate according to a ninthembodiment of the present invention.

FIG. 43 is a plan view of a light guide plate according to a tenthembodiment of the present invention.

FIG. 44 is a plan view of a light guide plate according to an eleventhembodiment of the present invention.

FIG. 45 is a plan view of a light guide plate according to a twelfthembodiment of the present invention.

FIG. 46 is a plan view of a light guide plate and LED boards accordingto a thirteenth embodiment of the present invention.

MODE FOR CARRYING OUT THE INVENTION First Embodiment

A first embodiment will be described with reference to FIGS. 1 to 21. Inthe following description, a liquid crystal display device 10 will bedescribed. X-axes, Y-axes and Z-axes may be specified in the drawings.The axes in each drawing correspond to the respective axes in otherdrawings. The vertical direction is defined based on FIGS. 3 to 5 andthe upper side and the lower side in those drawings correspond to thefront and the rear of the device.

As illustrated in FIG. 1, the liquid crystal display device 10 has arectangular overall shape in a plan view and includes a liquid crystaldisplay unit LDU, which is a core component. The liquid crystal displaydevice 10 includes a touchscreen 14, a cover panel (a protection panel,a cover glass) 15, and a case 16 fixed to the liquid crystal displayunit LDU. The liquid crystal display unit LDU includes a liquid crystalpanel (a display panel) 11, a backlight unit (a lighting device) 12, anda frame (a chassis component) 13. The liquid crystal panel 11 includes adisplay surface DS on the front side for displaying images. Thebacklight unit 12 is disposed behind the liquid crystal panel 11 andconfigured to emit light toward the liquid crystal panel 11. The frame13 presses down the liquid crystal panel 11 from the front side, thatis, a side opposite from the backlight unit 12 (a display surface DSside). The touchscreen 14 and the cover panel 15 are held in the frame13 that is a component of the liquid crystal display unit LDU from thefront and received by the frame 13 from the rear. The touchscreen 14 isdisposed more to the front than the liquid crystal panel 11 with apredefined distance apart from the liquid crystal panel 11. A platesurface of the touchscreen 14 on the rear (or on the inner side) is anopposed surface that is opposed to the display surface DS. The coverpanel 15 is disposed over the touchscreen 14 on the front and a platesurface thereof on the rear (or the inner side) is an opposed surfacethat is opposed to a plate surface of the touchscreen 14 on the front.An antireflective film AR is disposed between the touchscreen 14 and thecolor panel 15 (see FIG. 5). The case 16 is fixed to the frame 13 so asto cover the liquid crystal display unit LDU from the rear. Among thecomponents of the liquid crystal display device 10, a portion of theframe 13 (a rolled portion 13 b, which will be described later), thecover panel 15, and the case 16 form an appearance of the liquid crystaldisplay device 10. The liquid crystal display device 10 according tothis embodiment may be used for an electronic device such as asmartphone, a screen size of which is about 5 inches.

The liquid crystal panel 11 included in the liquid crystal display unitLDU will be described in detail. As illustrated in FIGS. 3 and 4, theliquid crystal panel 11 includes a pair of boards 11 a and 11 b and aliquid crystal layer (not illustrated). Each of the glass boards 11 aand 11 b is a substantially transparent glass board having a rectangularshape in a plan view and substantially transparent having high lighttransmissivity and high light transmissivity. The liquid crystal layeris between the boards 11 a and 11 b. The liquid crystal layer includesliquid crystal molecules that vary their optical characteristicsaccording to application of electrical field. The boards 11 a and 11 bare bonded together with a sealant, which is not illustrated, while apredefined gap corresponding to a thickness of the liquid crystal layeris maintained therebetween. The liquid crystal panel 11 includes adisplay area (a middle area surrounded by a plate surface light blockinglayer 32, which will be described later) and a non-display area (aperipheral area overlapping the plate surface light blocking layer 32,which will be described later). Images are displayed in the displayarea. The non-display area has a frame-like shape so as to surround thedisplay area. Images are not displayed in the non-display area. Along-side direction, a short-side direction, and a thickness directionof the liquid crystal panel 11 correspond with the X-axis direction, theY-axis direction, and the Z-axis direction, respectively.

One of the boards 11 a and 11 b on the front is a CF board 11 a and oneon the rear (or on the back) is an array board 11 b. On the innersurface of the array board 11 b (or on the liquid crystal layer side, aside opposed to the CF board 11 a), a number of thin film transistors(TFTs) that are switching components and a number of pixel electrodesare disposed. Gate lines and source lines are routed in a grid so as tosurround the TFTs and the pixel electrodes. Specific image signals aresupplied from a control circuit, which is not illustrated, to the lines.Each pixel electrode surrounded by the gate lines and the source linesis a transparent electrode of indium tin oxide (ITO) or zinc oxide(ZnO).

On the CF board 11 a, a number of color filters are disposed atpositions corresponding to pixels. The color filters are arranged suchthat three colors of R, G and B are repeatedly arranged. Between thecolor filters, a light blocking layer (a black matrix) is formed forreducing color mixture. A counter electrode that is opposed to the pixelelectrodes on the array board 11 b is on surfaces of the color filtersand the light blocking layer. The CF board 11 a is slightly smaller thanthe array board 11 b. On the inner surfaces of the boards 11 a and 11 b,alignment films for alignment of liquid crystal molecules in the liquidcrystal layer are formed, respectively. On the outer surfaces of theboards 11 a and 11 b, polarizing plates 11 c and 11 d are bonded,respectively (see FIG. 5).

Next, the backlight unit 12 included in the liquid crystal display unitLDU will be described in detail. As illustrated in FIG. 1, the backlightunit 12 has a rectangular block-like overall shape in a plan viewsimilar to the liquid crystal panel 11. As illustrated in FIGS. 2 to 4,the backlight unit 12 includes light emitting diodes (LEDs) 17, an LEDboard (a light source board) 18, a light guide plate 19, a reflectionsheet (a reflecting member) 40, an optical sheet (a light exiting-sideanisotropic light collector, an optical member) 20, a light blockingframe 21, a chassis 22, and a heat dissipation member 23. The LEDs 17are light sources. The LEDs 17 are mounted on the LED board 18. Thelight guide plate 19 guides light from the LEDs 17. The reflection sheet40 reflects light from the light guide plate 19. The optical sheet islayered on the light guide plate 19. The light blocking frame 21 holdsdown the light guide plate 19 from the front. The chassis 22 holds theLED board 18, the light guide plate 19, the optical sheet 20, and thelight blocking frame 21 therein. The heat dissipation member 23 ismounted so as to be in contact of the outer surface of the chassis 22.In the backlight unit 12, the LEDs 17 (the LED board 18) are disposed atone of the short sides of the periphery of the backlight unit 12.Namely, the backlight unit 12 is an edge-light type (or a side-lighttype) which uses a method of supplying light from one side.

As illustrated in FIGS. 2, 3, and 5, each LED 17 includes an LED chipthat is disposed on a board and sealed with a resin. The board is fixedto the LED board 18. Each LED chip mounted on the board has a mainwavelength of emitting light is one kind. Specifically, the LED chipthat emits light in a single color of blue is used. In the resin thatseals the LED chip, phosphors that emit a certain color of light whenexcited by the blue light emitted by the LED chip are dispersed. Anoverall color of light emitted by the phosphors is substantially white.The phosphors may be selected from yellow phosphors that emit yellowlight, green phosphors that emit green light, and red phosphors thatemit red light and used in a combination. Alternatively, the phosphorsin a single color may be used. A surface of each LED 17 is opposite froma mounting surface thereof that is mounted to the LED board 18 is alight emitting surface 17 a, that is, the LED 17 is a top surface lightemitting type.

As illustrated in FIGS. 2, 3, and 5, the LED board 18 has an elongatedplate-like shape that extends in the Y-axis direction (or the short-sidedirection of the light guide plate 19 or the chassis 22). The LED board18 is held in the chassis 22 with the plate surface thereof parallel tothe Y-Z plane, that is, perpendicular to the plate surface of the liquidcrystal panel 11 or the light guide plate 19. Namely, the LED board 18is held in a position such that the long-side direction and theshort-side direction of the plate surface thereof correspond with theY-axis direction and the Z-axis direction, respectively. Furthermore,the thickness direction thereof perpendicular to the plate surfacecorresponds with the X-axis direction. The LED board 18 is disposed suchthat a plate surface thereof facing the inner side (or a mountingsurface 18 a) is opposite one of short peripheral surfaces of the lightguide plate 19 (or a light entering surface 19 b, a light source opposedend surface) with a predefined distance therefrom in the X-axisdirection. An arrangement direction of the LEDs 17, the LED board 18,and the light guide plate 19 corresponds substantially with the X-axisdirection. The LED board 18 has a length about equal to or larger thanthe short dimension of the light guide plate 19. The LED board 18 ismounted to the one of the short ends of the chassis 22, which will bedescribed later.

As illustrated in FIG. 5, on the plate surface of the LED board 18 onthe inner side, that is, the plate surface facing the light guide plate19 (or the surface opposed to the light guide plate 19), the LEDs 17having the configuration described earlier are surface-mounted. Theplate surface is the mounting surface 18 a. The LEDs 17 are arranged inline (or linearly) on the mounting surface 18 a of the LED board 18 atpredefined intervals along the length direction thereof (or the Y-axisdirection). Namely, the LEDs 17 are arranged at intervals along theshort-side direction of the backlight unit 12 at one of the short endsof the backlight unit 12. The intervals (or arrangement pitches) of theLEDs 17 are about equal. Furthermore, on the mounting surface 18 a ofthe LED board 18, a trace (not illustrated) is formed from a metal film(e.g., a cupper film) for connecting the adjacent LEDs 17 in series. Thetrace extends along the Y-axis direction across the LEDs 17. Whenterminals formed at ends of the trace are connected to an external LEDdrive circuit, driving power is supplied to the LEDs 17. A base of theLED board 18 is made of metal similar to the chassis 22 and the trace(not illustrated) is formed on a surface of the base via an insulatinglayer. An insulating material such as ceramic may be used for the baseof the LED board 18.

The light guide plate 19 is made of substantially transparent syntheticresin (e.g., acrylic resin such as PMMA) having a refractive indexsufficiently larger than the refractive index of the air and high lighttransmissivity. As illustrated in FIGS. 2 and 6, the light guide plate19 has a substantially rectangular flat plate-like shape similar to theliquid crystal panel 11. The plate surface of the light guide plate 19is parallel to the plate surface (or the display surface DS) of theliquid crystal panel 11. The long-side direction and the short-sidedirection of the light guide plate 19 correspond with the X-axisdirection and the Y-axis direction, respectively. The thicknessdirection of the light guide plate 19 perpendicular to the plate surfacecorresponds with the Z-axis direction. As illustrated in FIGS. 3 and 4,the light guide plate 19 is disposed immediately below the liquidcrystal panel 11 and the optical sheet 20 inside the chassis 22. One ofthe short peripheral surfaces of the light guide plate 19 is oppositethe LEDs 17 on the LED board 18 at one of the short sides of the chassis22. The arrangement direction of the LEDs 17 (or the LED board 18) andthe light guide plate 19 corresponds with the X-axis direction. Thearrangement direction of the optical sheet (or the liquid crystal panel11) and the light guide plate 19 (or a direction in which they overlap)corresponds with the Z-axis direction. Namely, the arrangementdirections are perpendicular to each other. The light guide plate 19 hasa function of receiving light rays emitted from the LEDs 17 to the lightguide plate 19 along the X-axis direction (or the arrangement directionof the LEDs 17 and the light guide plate 19) through the shortperipheral surface, traveling the light rays therethrough, and guidingthe light rays toward the optical sheet 20 (or toward the front or thelight exiting side) so that the light rays exit from the plate surface.

As illustrated in FIGS. 3 and 4, the plate surface of the light guideplate 19 having a flat plate-like shape facing the front (or the lightexiting side) (the surface opposed to the liquid crystal panel 11 or theoptical sheet 20) is a light exiting surface 19 a through which thelight rays traveling therethrough exit toward the optical sheet 20 andthe liquid crystal panel 11. One of short peripheries (on the left inFIG. 3) of the light guide plate 19 adjacent to the plate surface havingan elongated shape along the Y-axis direction (or the arrangementdirection of the LEDs 17 or the long-side direction of the LED board 18)is opposed to the LEDs 17 (or the LED board 18) with a predefined gaptherebetween as illustrated in FIG. 5. The short peripheral surface isconfigured as a light entering surface through which the light rays fromthe LEDs 17 enter and an LED opposed peripheral surface (or a lightsource opposed peripheral surface) which is opposed to the LEDs 17. Thelight entering surface 19 b is parallel to the Y-Z plane andsubstantially perpendicular to the light exiting surface 19 a. Thearrangement direction of the LEDs 17 and the light entering surface 19 b(or the light guide plate 19) corresponds with the X-axis direction andparallel to the light exiting surface 19 a. The other one of the shortperipheral end surfaces of the light guide plate 19 farther from thelight entering surface 19 b described above (or a peripheral end surfaceopposite from the light entering surface 19 b) is referred to as anopposite end surface (or a non-light entering opposite surface) 19 d.Long peripheral end surfaces adjacent to the light entering surface 19 band the opposite end surface 19 d (or the peripheral end surfaces thatare opposite from each other and do not include the light enteringsurface 19 b) are referred to as peripheral end surfaces 19 e. Theperipheral end surfaces 19 e are surfaces parallel to the X-axisdirection (or the arrangement direction of the LEDs 17 and the lightguide plate 19) and the Z-axis direction. The peripheral end surfaces ofthe light guide plate 19 except for the light entering surface 19 b,that is, the opposite end surface 19 d and the peripheral end surfaces19 e are LED non-opposed peripheral end surfaces (light sourcenon-opposed peripheral end surfaces) which are not opposed to the LEDs17 as illustrated in FIGS. 3 and 4. The light rays emitted from the LEDs17 and entering the light guide plate 19 through the light enteringsurface 19 b that is a peripheral end surface of the light guide plate19 may be reflected by the reflection sheet 40, which will be describedlater, or totally reflected by the light exiting surface 19 a, anopposite plate surface 19 c, and other peripheries (the opposite endsurface 19 d and the peripheral end surfaces 19 e) and thus efficientlytransmitted through the light guide plate 19. If the light guide plate19 is made of acrylic resin such as PMMA, the refractive index is about1.49. Therefore, a critical angle may be about 42°. In the followingdescription, a direction along the peripheral end surfaces of the lightguide plate 19 opposite from each other and do not include the lightentering surface 19 b (or the long peripheral end surfaces, theperipheral end surfaces 19 e) (or the X-axis direction) is referred toas a “first direction.” A direction along the peripheral end surfacesopposite from each other and including the light entering surface 19 b(or the short peripheral end surfaces, the light entering surface 19 band the opposite end surface 19 d) (or the Y-axis direction) is referredto as a “second direction.” Furthermore, a direction normal to the platesurface of the light guide plate 19 (perpendicular to the firstdirection and the second direction) is referred to as a “thirddirection.”

As illustrated in FIGS. 3 and 4, among the plate surfaces of the lightguide plate 19, a plate surface facing the rear side (or an oppositeside from the light exiting side) (or a surface opposed to thereflection sheet 40 and a bottom plate 22 a of the chassis 22) isreferred to as the opposite plate surface 19 c. The reflection sheet 40is disposed on the opposite plate surface 19 c so as to cover an entirearea of the opposite plate surface. The reflection sheet 40 isconfigured to reflect the light rays from the light guide plate 19toward the front, that is, the light exiting surface 19 a. Namely, thereflection sheet 40 is sandwiched between the bottom plate 22 a of thechassis 22 and the light guide plate 19. The reflection sheet 40 isopposed to the opposite plate surface 19 c of the light guide plate 19.The reflection sheet 40 includes a reflection surface (or a reflectionmiller surface) 40 a for reflecting the light rays. The reflectionsurface 40 a of the reflection sheet 40 is silver and specularlyreflects light. The reflection sheet 40 may include a film base made ofsynthetic resin and a metal film (e.g., a silver thin film)vapor-deposited on a surface of the film base. As illustrated in FIG. 5,an end portion of the reflection sheet 40 closer to the light enteringsurface 19 b of the light guide plate 19 is outer than the lightentering surface 19 b, that is extends toward the LEDs 17. The extendingend portion reflects the light rays from the LEDs 17. According to theconfiguration, light entering efficiency at the light entering surface19 b improves.

As illustrated in FIGS. 3 and 7, the opposite plate surface 19 c of thelight guide plate 19 includes an exiting light reflecting portion 41 forreflecting the light rays traveling through the light guide plate 19such that the light rays exit from the light exiting surface 19 a. Theexiting light reflecting portion 41 is integrated with the light guideplate 19. The light guide plate 19 is prepared by injection molding. Apattern of the exiting light reflecting portion 41 is formed on aforming surface of a forming die for forming the opposite plate surface19 c. As illustrated in FIG. 9, the exiting light reflecting portion 41includes unit reflectors (exiting light unit reflectors) 41 a eachhaving a triangular cross-sectional shape (or a V-like cross-sectionalshape) and extending along the second direction (or the Y-axisdirection). The unit reflectors 41 a are arranged at intervals (i.e.,intermittently arranged) along the first direction (or the X-axisdirection). Each unit reflector 41 a includes a main reflecting surface41 a 1 and a reentering surface 41 a 2. The main reflecting surface 41 a1 is arranged on the LED 17 side (or the light entering surface 19 bside) with respect to the first direction. The reentering surface 41 a 2is arranged on the opposite side from the LED 17 side (or on theopposite end surface 19 d side). The main reflecting surface 41 a 1 is asloped surface that inclines such that the main reflecting surface 41 a1 becomes closer to the light exiting surface 19 a (or farther from theopposite plate surface 18 c) as a distance from the LED 17 increases (ora distance to the opposite end surface 19 d decreases) with respect tothe first direction. Each reentering surface 41 a 2 is a sloped surfacethat declines such that the reentering surface 41 a 2 becomes fartherfrom the light exiting surface 19 a (or closer to the opposite platesurface 19 c) as a distance from the LED 17 increases with respect tothe first direction. It is preferable to set an angle θs1 between themain reflecting surface 41 a 1 and the light exiting surface 19 a or theopposite plate surface 19 c in a range from 40° to 50°. In FIG. 9, theangle θs1 is about 45°. It is preferable to set an angle θs2 between thereentering surface 41 a 2 and the light exiting surface 19 a or theopposite plate surface 19 c in a range from 70° to 80°. In FIG. 9, theangle θs2 is about 80°. Namely, the angle θs1 of the main reflectingsurface 41 a 1 is smaller than the angle θs1 of the reentering surface41 a 2. The light rays are reflected by the main reflecting surface 41 a1 of the unit reflector 41 a arranged on the light entering surface 19 bwith respect to the first direction. According to the configuration, theangles of incidence of the light rays to the light exiting surface 19 ado not exceed the critical angle and thus the light rays are more likelyto exit from the light exiting surface 19 a. Regarding the reenteringsurface 41 a 2 of the unit reflector 41 a, the light rays having anglesof incidence smaller than the critical angle and passed through the mainreflecting surface 41 a 1 reenter the light guide plate 19 through thereentering surface 41 a 2. Heights (or dimensions in the thirddirection) of the unit reflectors 41 a, lines of which are arrangedalong the first direction, gradually increase and areas of the mainreflecting surfaces 41 a 1 and the reentering surfaces 41 a 2 increaseas a distance from the light entering surface 19 b (or the LEDs 17) withrespect to the first direction increases. According to theconfiguration, the light rays exiting from the light exiting surface 19a are controlled such that a uniform light distribution is achievedwithin the light exiting surface 19 a. The unit reflectors 41 a arearranged at substantially equal intervals with respect to the firstdirection regardless of the distance from the LEDs 17.

As illustrated in FIGS. 2 to 4, the optical sheet 20 has a rectangularshape in a plan view similar to the liquid crystal panel 11 and thechassis 22. The optical sheet 20 is disposed so as to cover the lightexiting surface 19 a of the light guide plate 19 from the front (or thelight exiting side). Because the optical sheet 20 is disposed betweenthe liquid crystal panel 11 and the light guide plate 19, the light raysexiting from the light guide plate 19 pass through the optical sheet 20.The optical sheet 20 directs the light rays toward the liquid crystalpanel 11 with specific optical properties added to the light rays whilepassing therethrough. The optical sheet 20 will be described in detaillater.

As illustrated in FIGS. 3 and 4, the light blocking frame 21 is formedin a frame-like (or a picture frame-like) shape that extends along theperiphery (or the peripheral end surfaces) of the light guide plate 19.The light blocking frame 21 presses down the periphery of the lightguide plate 19 for substantially the entire periphery. The lightblocking frame 21 is made of synthetic resin. The light blocking frame21 includes a surface in black, that is, has light blocking properties.The light blocking frame 21 is disposed such that an inner edge portion21 a thereof are arranged between the periphery of the light guide plate19 and LEDs 17 and the periphery (or the peripheral end surfaces) of theliquid crystal panel 11 and the periphery of the optical sheet 20 forthe entire periphery thereof. The light blocking frame 21 opticallyseparate those from one another. According to the configuration, thelight rays from the LEDs 17 and not entering the light guide plate 19through the light entering surface 19 b or the light rays leakingthrough the opposite end surface 19 d or the peripheral end surfaces 19e are blocked by the light blocking frame 21 and thus less likely todirectly enter peripheries (especially the peripheral end surfaces) ofthe liquid crystal panel 11 and the optical sheet 20. Each of three edgeportions of the light blocking frame 21 not overlapping the LEDs 17 andthe LED board 18 in a plan view (long edge portions and a short edgeportion farther from the LED board 18) includes a portion projectingfrom the bottom plate 22 a of the chassis 22 and a portion that supportsthe frame 13 from the rear. A short edge portion overlapping the LEDs 17and the LED board 18 in a plan view is formed so as to cover the end ofthe light guide plate 19 and the LED board 18 (or the LEDs 17) from thefront and bridge the long edge portions. The light blocking frame 21 isfixed to the chassis 22, which will be described next, with fixingmembers such as screws.

The chassis 22 is formed from a metal sheet having high thermalconductivity such as an aluminum sheet and an electrolytic zinc coatedsteel sheet (SECC). As illustrated in FIGS. 3 and 4, the chassis 22includes the bottom plate 22 a and side plates 22 b. The bottom plate 22a has a rectangular shape similar to the liquid crystal panel 11 in aplan view. The side plates 22 b project from outer edges (long edges andshort edges) of the bottom plate 22 a toward the front, respectively. Along-side direction and a short-side direction of the chassis 22 (or thebottom plate 22 a) correspond with the X-axis direction and the Y-axisdirection, respectively. A large portion of the bottom plate 22 a is alight guide plate holding portion 22 a 1 for supporting the light guideplate 19 from the rear (or an opposite side from the light exitingsurface 19 a). An end portion of the bottom plate 22 a closer to the LEDboard 18 is a board holding portion that protrudes toward the rear so asto form a step. As illustrated in FIG. 5, a board holding portion 22 a 2has an L-like cross section. The board holding portion 22 a 2 includes arising portion 38 and a holding bottom portion 39. The rising portion 38bends from an end of the light guide plate holding portion 22 a 1 andrises toward the rear. The holding bottom portion 39 bends from a distalend of the rising portion 38 and projects toward a side opposite fromthe light guide plate holding portion 22 a 1. A position at which therising portion 38 rises from the end of the light guide plate holdingportion 22 a 1 is farther from the LEDs 17 than the light enteringsurface 19 b of the light guide plate 19 (or closer to the middle of thelight guide plate holding portion 22 a 1). The long side plate 22 bbends and rises from the distal end of the holding bottom portion 39toward the front. The LED board 18 is mounted to the short side plate 22b continues to the board holding portion 22 a 2. The short side plate 22b is a board mounting portion 37. The board mounting portion 37 includesan opposed surface that is opposed to the light entering surface 19 b ofthe light guide plate 19. The LED board 18 is mounted to the opposedsurface. A plate surface of the LED board 18 opposite from the mountingsurface 18 a on which the LEDs 17 are mounted is fixed to an inner platesurface of the board mounting portion 37 with a board fixing member 25such as a double-sided tape. The mounted LED board 18 is arranged with asmall gap to the inner plate surface of the holding bottom portion 39 ofthe board holding portion 22 a 2. On the rear plate surface of thebottom plate 22 a of the chassis 22, a liquid crystal panel drivecircuit board (not illustrated) for controlling driving of the liquidcrystal panel 11, an LED drive circuit board (not illustrated) forsupplying driving power to the LEDs 17, and a touchscreen drive circuitboard (not illustrated) for controlling driving of the touchscreen 14are mounted.

The heat dissipation member 23 is formed from a metal sheet having highthermal conductivity such as an aluminum sheet. As illustrated in FIG.3, the heat dissipation member 23 extends along the short edge of thechassis 22, specifically, the board holding portion 22 a 2 for holdingthe LED board 18. As illustrated in FIG. 5, the heat dissipation member23 includes a first heat dissipation portion 23 a and a second heatdissipation portion 23 b. The first heat dissipation portion 23 a has anL-like cross section. The first heat dissipation portion 23 a isparallel to an outer surface of the board holding portion 22 a 2 and incontact with the outer surface. The second heat dissipation portion 23 bis parallel to an outer surface of the side plate 22 b that continues tothe board holding portion 22 a 2 (or the board mounting portion 37). Thefirst heat dissipation portion 23 a has an elongated flat plate-likeshape that extends along the Y-axis direction. A plate surface of thefirst heat dissipation portion 23 a facing the front and parallel to theX-Y plane is in contact with the outer surface of the holding bottomportion 39 of the board holding portion 22 a 2 for about the entirelength thereof. The first heat dissipation portion 23 a is fixed to theholding bottom portion 39 with screws SM. The first heat dissipationportion 23 a includes screw insertion holes 23 a 1 in which the screwsSM are inserted. The holding bottom portion 39 includes screw holes 28for the screws SM to be screwed. According to the configuration, heatfrom the LEDs 17 are transmitted to the first heat dissipation portion23 a via the LED board 18, the board mounting portion 37, and the boardholding portion 22 a 2. The screws SM are arranged at intervals alongthe extending direction of the first heat dissipation portion 23 a andfixed thereto. The second heat dissipation portion 23 b has an elongatedflat plate-like shape that extends along the Y-axis direction. A platesurface of the second heat dissipation portion 23 b facing the innerside and parallel to the Y-Z plane is arranged opposite the outer platesurface with a predefined gap between the plate surface and the outerplate surface of the board mounting portion 37.

Next, the frame 13 included in the liquid crystal display unit LDU willbe described. The frame 13 is made of metal having high thermalconductivity such as aluminum. As illustrated in FIG. 1, the frame 13has a rectangular frame-like (or a picture frame-like) overall shapealong the peripheries (or the outer edge portions) of the liquid crystalpanel 11, the touchscreen 14, and the cover panel 15 in a plan view. Theframe 13 may be prepared by stamping. As illustrated in FIGS. 3 and 4,the frame 13 holds down the periphery of the liquid crystal panel 11 andholds the liquid crystal panel 11, the optical sheet 20, and the lightguide plate 19, which are layered, together with the chassis 22 of thebacklight unit 12. The frame 13 receives the peripheries of thetouchscreen 14 and the cover panel 15 from the rear. The frame 13 isdisposed between the peripheries of the liquid crystal panel 11 and thetouchscreen 14. According to the configuration, a predefined gap isprovided between the liquid crystal panel 11 and the touchscreen 14.Even if the touchscreen 14 is pushed by the cover panel 15 when anexternal force is applied to the cover panel 15 and deformed toward theliquid crystal panel 11, the deformed touchscreen 14 is less likely toaffect the liquid crystal panel 11.

As illustrated in FIGS. 3 and 4, the frame 13 includes a frame portion(or a frame base portion, a picture frame-like portion) 13 a, a rolledportion (or a tubular portion) 13 b, and mounting plate portions 13 c.The frame portions 13 a are along the peripheries of the liquid crystalpanel 11, the touchscreen 14, and the cover panel 15. The rolled portion13 b continues from the outer edge of the frame portion and surroundsthe touchscreen 14, the cover panel 15, and the case 16 from the outerside. The mounting plate portions 13 c project from the frame portion 13a toward the rear. The mounting plate portions 13 c are mounted to thechassis 22 and the heat dissipation member 23. The frame portion 13 ahas a rectangular frame-like shape in a plan view including platesurfaces having flat plate-like shapes and parallel to the platesurfaces of the liquid crystal panel 11, the touchscreen 14, and thecover panel 15. An outer peripheral portion 13 a 2 of the frame portion13 a has a thickness larger than a thickness of an inner peripheralportion 13 a 1 thereof. A gap GP is provided at a boundary between theinner peripheral portion 13 a 1 and the outer peripheral portion 13 a 2.The inner peripheral portion 13 a 1 of the frame portion 13 a isdisposed between the periphery of the liquid crystal panel 11 and theperiphery of the touchscreen 14. The outer peripheral portion 13 a 2receives the periphery of the cover panel 15 from the rear. Because thefront plate surface of the frame portion 13 a is covered with the coverpanel 15 for about the entire area thereof, the front surface is lesslikely to be exposed to the outside. According to the configuration,even if a temperature of the frame 13 increases due to the heat from theLEDs 17, a user of the liquid crystal display device 10 is less likelyto directly touch a portion of the frame 13 exposed to the outside. Thisconfiguration is advantageous in terms of safety. As illustrated in FIG.5, a shock absorber 29 is fixed to the rear plate surface of the innerperipheral portion 13 a 1 of the frame portion 13 a. The shock absorber29 is for pressing down the periphery of the liquid crystal panel 11from the front and absorbing an impact that may be applied to theperiphery of the liquid crystal panel 11. A first fixing member 30 isfixed to the front plate surface of the inner peripheral portion 13 a 1for fixing the periphery of the touchscreen 14 and absorbing an impactthat may be applied to the periphery of the touchscreen 14. The shockabsorber 29 and the first fixing member 30 are arranged at a positionwithin the inner peripheral portion 13 a 1 overlapping each other in aplan view. A second fixing member 31 is fixed to the front plate surfaceof the outer peripheral portion 13 a 2 of the frame portion 13 a forfixing the periphery of the cover panel 15 and absorbing an impact thatmay be applied to the periphery of the cover panel 15. The shockabsorber 29 and the fixing members 30 and 31 are disposed so as toextend along the sides of the frame portion 13 a except for fourcorners. The fixing members 30 and 31 may be double-side tapes thatincludes base materials having cushioning properties.

As illustrated in FIGS. 3 and 4, the rolled portion 13 b includes afirst rolled portion 34 and a second rolled portion 35. The first rolledportion 34 has a short rectangular tubular overall shape in a plan viewand projects from an outer peripheral edge of the outer peripheralportion 13 a 2 of the frame portion 13 a toward the front. The secondrolled portion 35 projects from the outer peripheral edge of the outerperipheral portion 13 a 2 of the frame portion 13 a toward the rear.Namely, the outer edge of the frame portion 13 a continues to the innersurface of the rolled portion 13 b having a short rectangular tubularshape at about the middle of the inner surface with respect the axialdirection (or the Z-axis direction) for the entire periphery of therolled portion 13 b. An inner periphery of the first rolled portion 34is opposed to the peripheries of the touchscreen 14 and the cover panel15. An outer periphery of the first rolled portion 34 is exposed to theoutside of the liquid crystal display device 10, that is, formsappearances of sides of the liquid crystal display device 10. The secondrolled portion 35 covers front edges (or a mounting portion 16 c) of thecase 16 that is disposed behind the frame portion 13 a from peripheralsides. An inner periphery of the second rolled portion 35 is opposed tothe mounting portion 16 c of the case 16, which will be described later.An outer periphery of the second rolled portion 35 is exposed to theoutside of the liquid crystal display device 10, that is, formsappearances of sides of the liquid crystal display device 10. The secondrolled portion includes a frame-side fixing portion 35 a having ahook-like cross section at a distal end thereof. The case 16 is held tothe frame-side fixing portion 35 a to maintain the case 16 being fixed.

As illustrated in FIGS. 3 and 4, the mounting plate portions 13 cproject from the outer peripheral portion 13 a 2 of the frame portion 13a toward the rear and has a plate-like shape that extends along thesides of the frame portion 13 a. Plate surface of the mounting plateportions 13 c are substantially perpendicular to the plate surface ofthe frame portion 13 a. The mounting plate portions 13 c are arranged atthe respective sides of the frame portion 13 a. The mounting plateportion 13 c at the short side of the frame portion 13 a on the LEDboard 18 side is mounted such that the inner plate surface thereof is incontact with the outer plate surface of the second heat dissipationportion 23 b of the heat dissipation member 23. The mounting plateportions 13 c are fixed to the second heat dissipation portion 23 b withscrews SM. The mounting plate portions 13 c include screw insertionholes 13 c 1. The second heat dissipation portion 23 b includes screwholes 36 for the screws SM to be fixed. Heat from the LEDs 17transmitted from the first heat dissipation portion 23 a to the secondheat dissipation portion 23 b is transmitted to the mounting plateportions 13 c and then to the entire area of the frame 13. According tothe configuration, the heat is efficiently dissipated. The mountingplate portion 13 c is indirectly fixed to the chassis 22 via the heatdissipation member 23. The mounting plate portion 13 c at the short sideof the frame portion 13 a farther from the LED board 18 and the mountingplate portions 13 c at the long sides of the frame portion 13 a arefixed with the screws SM such that the inner plate surface thereof is incontact with the outer plate surfaces of the side plates 22 b of thechassis 22. The mounting plate portions 13 c include the screw insertionholes 13 c 1 in which the screws SM are inserted. The side plates 22 binclude screw holes 36 for the screws SM to be fixed. The screws SM arearranged along the extending direction of each mounting plate portion 13c at intervals and fixed to the mounting plate portions 13 c.

Next, the touchscreen 14 fixed to the frame 13 the is described abovewill be described. As illustrated in FIGS. 1, 3 and 4, the touchscreen14 is a position input device through which the user can inputinformation regarding positions within the display surface DS of theliquid crystal panel 11. The touchscreen 14 has a rectangular shape. Thetouchscreen 14 includes a glass substrate that is substantiallytransparent and has high light transmissivity and a predefinedtouchscreen pattern (not illustrated) formed on the substrate.Specifically, the touchscreen 14 includes a glass substrate having arectangular shape similar to the liquid crystal panel 11 in a plan viewand a touchscreen transparent electrode (not illustrated) formed thefront plate surface of the substrate. The touchscreen transparentelectrodes are the touchscreen pattern using the projected capacitivetouchscreen technology. A number of the touchscreen transparentelectrodes are arranged in a grid within the plate surface of thesubstrate. Terminals (not illustrated) are formed in one of short edgeportions of the touchscreen 14. The terminals are connected to tracescontinue from the touchscreen transparent electrodes that are portionsof the touchscreen pattern. A flexible printed circuit board, which isnot illustrated, is connected to the terminals. Electrical potentialsare applied to the touchscreen transparent electrodes of the touchscreenpattern by a touchscreen drive circuit board. As illustrated in FIG. 5,the inner plate surface of the touchscreen 14 at the periphery thereofis fixed to the inner peripheral portion 13 a 1 of the frame portion 13a of the frame 13 with the first fixing member 30 that is describedearlier while they are opposed each other.

Next, the cover panel 15 mounted to the frame 13 will be described. Asillustrated in FIGS. 1, 3 and 4, the cover panel 15 covers the entirearea of the touchscreen 14 from the front to protect the touchscreen 14and the liquid crystal panel 11. The cover panel 15 covers the entirearea of the frame portion 13 a of the frame 13 from the front and formsa front appearance of the liquid crystal display device 10. The coverpanel 15 has a rectangular shape in a plan view. The cover panel 15includes a base in a plate-like shape and made of transparent glasshaving high light transmissivity, preferably, toughened glass.Chemically toughened glass may be preferable for the tempered glass usedfor the cover panel 15. The chemically toughened glass includes achemically toughened layer formed through a chemical toughening processon a surface of the glass base having a plate-like shape. The chemicaltoughening process may be a process for toughening a glass base having aplate-like shape by replacing alkali metal ions included in glassmaterial with alkali metal ions each having a larger diameter by alkalimetal ion exchange. The chemically toughened layer formed as above is acompressive stress layer (ion exchange layer) in which compressionstress remains. Because the cover panel 15 has mechanical strength andhigh shock resistance, the cover panel 15 more properly protects thetouchscreen 14 and the liquid crystal panel 11 disposed behind the coverpanel 15 from break or damage.

As illustrated in FIGS. 3 and 4, the cover panel 15 has a rectangularshape similar to the liquid crystal panel 11 and the touchscreen 14 in aplan view. A size of the cover panel 15 in a plan view is slightlylarger than those of the liquid crystal panel 11 and the touchscreen 14.The cover panel 15 includes a projecting portion 15EP that projectoutward over the peripheries of the liquid crystal panel 11 and thetouchscreen 14 for the entire periphery, that is, the projecting portion15EP has an eaves-like shape. The projecting portion 15EP has arectangular frame-like shape (or a picture frame-like shape) whichsurrounds the liquid crystal panel 11 and the touchscreen 14. Asillustrated in FIG. 5, an inner plate surface of the projecting portion15EP is fixed to the outer peripheral portion 13 a 2 of the frameportion 13 a of the frame 13 with the second fixing member 31 describedearlier while they are opposed each other. A middle portion of the coverpanel 15 opposite the touchscreen 14 is layered on the touchscreen 14 onthe front via the antireflective film AR.

Aa illustrated in FIGS. 3 and 4, a plate surface light blocking layer(or a light blocking layer, a plate surface light blocking portion) 32is formed on an inner plate surface (or a rear plate surface, a platesurface opposed to the touchscreen 14) of the cover panel 15 thatincludes the projecting portion 15EP at the outer periphery. The platesurface light blocking layer 32 is made of light blocking material suchas black paint. The plate surface light blocking layer 32 is formed byprinting the light blocking material on the inner plate surface and thusintegral with the plate surface. For forming the plate surface lightblocking layer 32, printing including screen printing and inkjetprinting may be used. The plate surface light blocking layer 32 isformed in the entire area of the projecting portion 15EP and an areathat overlap the peripheries of the touchscreen and the liquid crystalpanel 11 in a plan view. Namely, the plate surface light blocking layer32 is formed so as to surround the display area of the liquid crystalpanel 11. Therefore, light rays outside the display area are blocked bythe plate surface light blocking layer 32 and thus images are displayedin the display area with high display quality.

Next, the case 16 mounted to the frame 13 will be described. The case 16is made of synthetic resin or metal. As illustrated in FIGS. 1, 3 and 4,the case 16 has a bowl-like shape with an opening on the front andcovers the frame portion 13 a and the mounting plate portions 13 c ofthe frame 13, the chassis 22, and the heat dissipation member 23 fromthe rear and forms a rear appearance of the liquid crystal displaydevice 10. The case 16 includes a bottom portion 16 a, a curved portion16 b, and the mounting portion 16 c. The bottom portion 16 a issubstantially flat. The curved portion 16 b curves from a boundary ofthe bottom portion 16 a toward the front and has a curved cross section.The mounting portion 16 c projects from a boundary of the curved portion16 b substantially straight toward the front. The mounting portion 16 cincludes a case-side fixing portion 16 d having a hook-like crosssection. The case-side fixing portion 16 d is hooked to a frame-sidefixing portion 35 d of the frame 13. According to the configuration, thecase 16 is maintained fixed to the frame 13.

As illustrated in FIG. 3, the light guide plate 19 included in thebacklight unit 12 having the above configuration includes the exitinglight reflecting portion 41 for reflecting light rays traveling throughthe light guide plate 19 to increase rays of light exiting through thelight exiting surface 19 a. Light collecting effects are selectivelyadded to the light rays reflected by the exiting light reflectingportion 41 and the angles of incidence to the light exiting surface 19 aare less likely to be smaller than the critical angle. Therefore, morelight rays exit. Detailed configurations regarding the exiting lightreflecting portion 41 will be described later.

The backlight unit 12 in this embodiment has a configuration forcollecting rays of exiting light with respect to the second direction(or the Y-axis direction). The configuration and a reason why it hassuch a configuration will be described. As illustrated in FIGS. 3 and 5,light rays traveling through the light guide plate 19 may be reflectedby the unit reflectors 41 a of the exiting light reflecting portion 41.The angles of incidence of the light rays entering to the light exitingsurface 19 a are equal to or smaller than the critical angle and thelight rays exit from the light exiting surface 19 a. With respect to thefirst direction (or the X-axis direction), the light rays are reflectedtoward the front by the unit reflector 41 a, that is, the light rays arecollected so as to travel from the light exiting surface 19 a toward thefront along the normal direction. The exiting light reflecting portion41 adds the light collecting effects to the reflected light rays withrespect to the first direction but less likely to add the lightcollecting effects to the reflected light rays with respect to thesecond direction. Therefore, brightness anisotropy may occur in lightexiting from the light exiting surface 19 a. This embodiment has thefollowing configuration to collect the light rays with respect to thesecond direction. As illustrated in FIG. 2, the optical sheet 20includes a prism sheet (light exiting-side anisotropic light collectingportion) 42 having light collecting anisotropy for selectively addingthe light collecting effects to the transmitted light rays with respectto the second direction. The opposite plate surface 19 c of the lightguide plate 19 includes the prism portion (the opposite platesurface-side prism portion) 43 having light collecting anisotropy forselectively adding the light collecting effects to the light raysreflected by the exiting light reflecting portion 41 with respect to thesecond direction.

The LEDs 17 are arranged at intervals with respect to the seconddirection, that is, the longitudinal direction of the light enteringsurface 19 b of the light guide plate 19. Mixture of the light raysemitted by the LEDs 17 and entering the light entering surface 19 b tendto be insufficient on a side closer to the light entering surface 19 bwith respect to the first direction. Uneven brightness with respect tothe second direction tends to occur in the light exiting from the lightexiting surface 19 a. In this embodiment, the uneven brightness of theexiting light with respect to the second direction is compensated by theconfiguration described below. As illustrated in FIG. 2, the prismportion 43 is formed on the opposite plate surface 19 c of the lightguide plate 19. The prism portion 43 is for totally reflecting the lightrays traveling through the light guide plate 19 to diffuse the lightrays with respect to the second direction. The concave lenticular lensportion (the lenticular lens portion, the light exiting surface-sidelenticular lens portion) 44 is formed on the light exiting surface 19 aof the light guide plate 19. The concave lenticular lens portion 44 isfor totally reflecting the light rays traveling through the light guideplate 19 to diffuse the light rays with respect to the second direction.Next, the prism sheet 42, the prism portion 43, and the concavelenticular lens portion 44 will be described.

As illustrated in FIGS. 2 and 10, the prism sheet 42 includes a sheetbase 42 b and light exiting-side unit prisms (light exiting-side unitcollectors) 42 a. The sheet base 42 b has a sheet shape. The sheet base42 b includes a light entering-side plate surface 42 b 1 and a lightexiting-side plate surface 42 b 2. The light exiting from the lightguide plate 19 enters through the light entering-side plate surface 42 b1. The light exiting-side plate surface 42 b 2 is located on an oppositeside (or the light exiting side) from the light entering-side platesurface 42 b 1. The light exiting-side unit prisms 42 a are formed onthe light exiting-side plate surface 42 b 2. The light exiting-side unitprisms 42 a have light collecting anisotropic properties. The sheet base42 b is made of substantially transparent synthetic resin, specifically,thermosetting resin such as PET. The refractive index of the resin isabout 1.667. The light exiting-side unit prisms 42 a are integrallyformed with the light exiting-side plate surface 42 b 2, which is thefront plate surface (or on the light exiting side) of the sheet base 42b. The light exiting-side unit prisms 42 a are made of transparentultraviolet curing resin, which is one kind of light curing resin. Inthe production of the prism sheet 42, an ultraviolet curing resin thatis not cured is inserted in a forming die to fill the die and then thesheet base 42 b is placed over an opening of the die such that theultraviolet curing resin that is not cured is in contact with the lightexiting-side plate surface 42 b 2. Ultraviolet rays are applied to theultraviolet curing resin via the sheet base 42 b in the above condition.When the ultraviolet curing resin is cured, the light exiting-side unitprisms 42 a are integrally formed with the sheet base 42 b. Theultraviolet curing resin used for the light exiting-side unit prisms 42a may be acrylic resin such as PMMA. The refractive index of the resinmay be about 1.59. The light exiting-side unit prisms 42 a project fromthe light exiting-side plate surface 42 b 2 of the sheet base 42 btoward the front (or the light exiting side) along the third direction(or the Z-axis direction). Each light exiting-side unit prism 42 a has asubstantially triangular cross section along the second direction (orthe Y-axis direction) and linearly extends along the first direction (orthe X-axis direction). Multiple light exiting-side unit prisms 42 a arearranged along the second direction on the light exiting-side platesurface 42 b 2. The widths (or the dimensions in the second direction)of the light exiting-side unit prisms 42 a are the same for an entirelength with respect to the first direction. Each light exiting-side unitprism 42 a has an isosceles triangular cross section including a pair ofslopes 42 a 1 and a vertex angle θv1 of about 90° (a right angle). Thelight exiting-side unit prisms 42 a arranged along the second directioninclude vertex angles θv1 about equal to one another, widths of bottomsurfaces 42 a 2 about equal to one another, and heights about equal toone another. Intervals of the light exiting-side unit prisms 42 a areabout equal to one another.

When light rays from the light guide plate 19 enter the prism sheet 42having the above configuration, as illustrated in FIG. 10, the lightrays enter the light entering-side plate surface 42 b 1 of the sheetbase 42 b via an air layer between the light exiting surface 19 a of thelight guide plate 19 and the sheet base 42 b of the prism sheet 42. Thelight rays are refracted at interfaces with angles in response to anglesof incidence. If the light rays transmitted through the lightexiting-side unit prisms 42 a have reached the slope surfaces 42 a 1 ofthe light exiting-side unit prisms 42 a and the angles of incidencethereof are larger than the critical angle, the light rays are totallyreflected and returned to the sheet base 42 b (retroreflected). If theangles of incidence are smaller than the critical angle, the light raysare not reflected at the interfaces and thus exit. The light raystraveling toward the adjacent light exiting side-unit prisms 42 a amongthe light rays exiting from the slope surfaces 42 a 1 of the lightexiting-side unit prisms 42 a enter the light exiting-side unit prisms42 a and return to the sheet base 42 b. The light rays exiting from thelight exiting-side unit prisms 42 a are controlled to travel indirections closer to a frontward direction toward the front with respectto the second direction. Namely, light collecting effects areselectively added to the exiting light with respect to the seconddirection.

Next, the prism portion 43 on the opposite plate surface 19 c of thelight guide plate 19 will be described. The prism portion 43 isintegrally formed with the light guide plate 19. To integrally form theprism portion 43 with the light guide plate 19, the light guide plate 19may be prepared by injection molding with a forming die including aforming surface for forming the opposite plate surface 19 c with apattern of the prism portion 43. As illustrated in FIGS. 2, 7 and 10,the prism portion 43 includes the unit prisms (opposite platesurface-side unit prisms) 43 a arranged along the second direction (orthe Y-axis direction). Each unit prism 43 a extends along the firstdirection (or the X-axis direction). The unit prisms 43 a project fromthe opposite plate surface 19 c toward the front (or the light exitingside) along the third direction (or the Z-axis direction). Each unitprism 43 a has a substantially triangular cross section along the seconddirection and linearly extends along the first direction. Widths (ordimensions in the second direction) of the unit prisms 43 a are equal toone another for the entire length with respect to the first direction.Each unit prism 43 a has an isosceles triangular cross section includinga pair of slope surfaces 43 a 1 and a vertex angle θv2 larger than 90°(an obtuse angle). Preferably, the vertex angle θv2 is in a range from100° to 150°, most preferably, about 140°. Namely, the vertex angle θv2of each unit prism 43 a is larger than the vertex angle θv1 of eachlight exiting-side unit prism 42 a. The unit prisms 43 a arranged alongthe second direction include vertex angles θv2 about equal to oneanother, widths of bottom surfaces about equal to one another, andheights about equal to one another. Intervals of the unit prisms 43 aare about equal to one another.

As illustrated in FIG. 10, the prism portion 43 having the aboveconfiguration add the optical effects to the light rays travelingthrough the light guide plate 19 and reached the opposite plate surface19 c as follows. If the light rays that have reached the opposite platesurface 19 c enter the slope surfaces 43 a 1 of the unit prisms 43 awith angles of incidence smaller than the critical angle, at least somelight rays are refracted at the slope surfaces 43 a 1 and selectivelycollected with respect to the second direction. Then, the collectedlight rays exit the unit prisms 43 a. The light rays that have exitedthe unit prisms 43 a are reflected by the reflection surface 40 a of thereflection sheet 40. The reflected light rays that have reached theopposite plate surface 19 c enter the slope surfaces 43 a 1 of the unitprisms 43 a. Some light rays are refracted, that is, selectivelycollected with respect to the second direction. The light rays to whichthe light collecting effects are added by the prism portion 43 are morelikely to be collected with respect to the second direction at the prismsheet 42. According to the configuration, frontward brightness relatedto the light rays exiting from the prism sheet 42 improves. Opticaleffects for diffusing the light rays with respect to the seconddirection may be added to some light rays refracted at the slopesurfaces 43 a 1 of the unit prisms 43 a to which the anisotropic lightcollecting effects described above are not added. If the light rays thathave reached the opposite plate surface 19 c enter the slope surfaces 43a 1 of the unit prisms 43 a with the angles of incidence larger than thecritical angle, the light rays are totally reflected by the slopesurfaces 43 a 1. The light rays that are totally reflected by the slopesurfaces 43 a 1 of the unit prisms 43 a travel through the light guideplate 19 to be diffused with respect to the second direction. The lightrays are reflected by the exiting light reflecting portion 41.Therefore, uneven brightness with respect to the second direction isless likely to occur in the light exiting from the light exiting surface19 a.

Next, the concave lenticular lens portion 44 on the light exitingsurface 19 a side of the light guide plate 19 will be described. Theconcave lenticular lens portion 44 is integrally formed with the lightguide plate 19. To integrally form the concave lenticular lens portion44 with the light guide plate 19, the light guide plate 19 may beprepared by injection molding with a forming die including a formingsurface for the light exiting surface 19 a with a pattern of the concavelenticular lens portion 44. As illustrated in FIGS. 2, 6 and 10, theconcave lenticular lens portion 44 includes concave cylindrical lenses(cylindrical lenses, light exiting surface-side cylindrical lenses) 44 athat extend along the first direction (or the X-axis direction). Theconcave cylindrical lenses 44 a are arranged along the second direction(or the Y-axis direction) in the light exiting surface 19 a. The concavecylindrical lenses 44 a are concave lenses formed by recessing the lightexiting surface 19 a along the third direction (or the Z-axis direction)toward the rear side. Each concave cylindrical lens 44 a has a grooveshape that extends along the first direction with a semicircular crosssection along the second direction. Each concave cylindrical lens 44 aincludes a concave surface 44 a 1. Each concave cylindrical lens 44 ahas the following configuration. When an angle θt of a tangent line Taat a base section 44 a 2 of the concave surface 44 a 1 relative to thesecond direction is referred to as “a tangent angle,” the tangent angleθt may be about 70°. The detailed configuration of the concavelenticular lens portion 44 will be described later.

As illustrated in FIG. 10, the concave cylindrical lenses 44 a havingthe above configuration add optical effects to light rays that havetraveled through the light guide plate 19 and reached the light exitingsurface 19 a as follows. If the light rays that have reached the lightexiting surface 19 a enter the concave surfaces 44 a 1 with angles ofincidence larger than the critical angle, the light rays are totallyreflected by the concave surfaces 44 a 1. The reflected light raystravel through the light guide plate 19 so as to be diffused withrespect to the second direction. In comparison to convex cylindricallenses, the light rays are more likely to enter the concave surfaces 44a 1 of the concave cylindrical lenses 44 a with the angles of incidencelarger than the critical angle. Therefore, the concave cylindricallenses 44 a are more likely to totally reflect the light rays and thusthe light rays are diffused in a wider area with respect to the firstdirection. The light reflected by the exiting light reflecting portion41 and exiting from the light exiting surface 19 a are less likely tohave uneven brightness with respect to the second direction. If thelight rays that have reached the light exiting surface 19 a enter theconcave surfaces 44 a 1 of the concave cylindrical lenses 44 a with theangles of incidence equal to or smaller than the critical angle, atleast some of the light rays are refracted at the concave surfaces 44 a1 exit toward the prism sheet 42 with the light collecting effects withrespect to the second direction selectively added to the light rays. Thelight rays with the anisotropic light collecting effects added by theconcave cylindrical lenses 44 a are less likely to be collected by theprism sheet 42 with respect to the second direction. The light rays aremore likely to be diffused with respect to the second direction.Although the light can improve the uneven brightness of the lightexiting from the prism sheet 42, the light cannot contribute to theimprovement of the frontward brightness.

As illustrated in FIGS. 9 and 10, the light rays emitted by the LEDs 17and entering the light guide plate 19 through the light entering surface19 b as described above travel through the light guide plate 19 towardthe opposite end surface 19 d with respect to the first direction.During traveling through the light guide plate 19, the light rays aretotally reflected by the prism portion 43 on the opposite plate surface19 c and the concave lenticular lens portion 44 in the light exitingsurface 19 a, that is, the light rays are diffused in the wide area withrespect to the second direction. The light rays traveling through thelight guide plate 19 are properly mixed with respect to the seconddirection, which corresponds to the arrangement direction of the LEDs17. Therefore, the light exiting from the light exiting surface 19 a isless likely to have uneven brightness with respect to the seconddirection. At least some of the light rays reflected by the exitinglight reflecting portion 41 during traveling through the light guideplate 19 exit from the light exiting surface 19 a with the lightcollecting effects selectively added by either the prism portion 43 orthe concave lenticular lens portion 44 or both. The light rays with theanisotropic light collecting effects added by the concave lenticularlens portion 44 are less likely to be collected by the prism sheet 42with respect to the second direction. However, the light rays with theanisotropic light collecting effects added not by the concave lenticularlens portion 44 but by the prism portion 43 are more likely to becollected by the prism sheet 42 with respect to the second direction.Therefore, the frontward brightness related to the light exiting fromthe prism sheet 42 improves.

As illustrated in FIG. 10, the prism sheet 42 includes the lightexiting-side unit prisms 42 a having the vertex angles θv1 smaller thanthe vertex angles θv2 of the unit prisms 43 a. In comparison to theprism portion 43, the prism sheet 42 retroreflects more light rays andrestricts the range of the angles of emergence of the exiting light to asmaller range. Namely, the prism sheet 42 has the strongest lightcollecting effects. The anisotropic light collecting effects are addedto some light rays entering the prism sheet 42 by the prism portion 43at the opposite plate surface 19 c of the light guide plate 19.Therefore, a percentage of the light rays that are retroreflected by thelight exiting-side unit prisms 42 a of the prism sheet 42 is low andthus the light rays efficiently exit from the light exiting-side unitprisms 42 a. According to the configuration, high light use efficiencyis achieved. This configuration is preferable for improving thebrightness of light exiting from the backlight unit 12.

The following examination was performed to determine angles of the lightrays entering the prism sheet 42 for contribution of the light raysexiting from the prism sheet 42 to the improvement of the frontwardbrightness. A relationship between the angles of incidence of the lightrays entering the light entering-side plate surface 42 b 1 of the sheetbase 42 b of the prism sheet 42 and the angles of emergence of the lightrays exiting from the prism sheet 42 is determined based on Snell's law.Results are presented in FIG. 13. A specific method of calculation isprovided below. An angle of emergence of each light ray exiting from thelight entering-side plate surface 42 b 1 is calculated based on an angleof incidence of the light ray entering the light entering-side platesurface 42 b 1. The angle of emergence of light ray exiting from thelight entering-side plate surface 42 b 1 is equal to the angle ofincident of light entering the light exiting-side plate surface 42 b 2or the bottom surface 42 a 2 of the light exiting-side unit prism 42 a.Therefore, an angle of emergence of light ray exiting from the lightexiting-side plate surface 42 b 2 and an angle of emergence of light rayexiting from the bottom surface 42 a 2 of the light exiting-side unitprism 42 a can be calculated (see FIG. 10). The angle of emergence ofthe light ray exiting from the light exiting-side plate surface 42 b 2or the angle of emergence of the light ray exiting from the bottomsurface 42 a 2 of the light exiting-side unit prism 42 a is equal to anangle of incidence of the light ray entering the slope surface 42 a 1 ofthe light exiting-side unit prism 42 a (see FIG. 10). The refractiveindexes of the sheet base 42 b and the light exiting-side unit prisms 42a and the vertex angles θv1 of the light exiting-side unit prisms 42 ahave been described earlier. The refractive index of the external airlayer is set to “1.0.” In FIG. 13, the vertical axis represents anglesof incidence of light rays entering the light entering-side platesurface 42 b 1 of the sheet base 42 b (in unit of “°”) and thehorizontal axis represents angles of emergence of light rays exitingfrom the slope surface 42 a 1 of the light exiting-side unit prism 42 a.The light rays with the angle of refraction of 0° travel in thedirection parallel to the frontward direction toward the front.According to FIG. 13, to achieve light rays exiting from the slopesurfaces 42 a 1 of the light exiting-side unit prisms 42 a with angleswithin in a range of ±10°, the angles of incidence of the light raysentering the light entering-side plate surface 42 b 1 of the sheet base42 b need to be set in a range from 23° to 40°. If the light raysentering the prism sheet 42, that is, the light rays exiting from thelight exiting surface 19 a of the light guide plate 19 are controlled toexit with the angles of emergence in the range from 23° to 40°, thelight rays exit from the light exiting-side unit prisms 42 a of theprism sheet 42 with the angles of emergence in the range of ±10°relative to the frontward direction. This is effective for improving thefrontward brightness related to the exiting light. In this embodiment,the light rays to which the anisotropic light collecting effects areadded by the prism portion 43 of the light guide plate 19 tend toinclude a larger number of light rays exiting from the light exitingsurface 19 a with the angles of emergence in the range from 23° to 40°.Furthermore, the light rays to which the anisotropic light collectingeffects are added by the concave lenticular lens portion 44 tend toinclude a larger number of light rays exiting from the light exitingsurface 19 a with the angles of emergence out of the range from 23° to40°.

In the known technology, elongated protrusions are formed on the lightexiting surface of the light guide plate to improve the frontwardbrightness of exiting light. However, uneven brightness is more likelyto occur according to the above configuration. In the known technology,point light sources are arranged at intervals along a longitudinaldirection of the light entering surface of the light guide plate. In aportion of the light guide plate closer to the light entering surface,bright spots and dark spots tend to be created by the light exiting fromthe light exiting surface along the arrangement direction of the pointlight sources. The elongated protrusions tend to increase the brightnessin the bright spots and thus the uneven brightness is more likely tooccur in the portion close to the light entering surface. If cylindricallenses are formed instead of the elongated protrusions, the unevenbrightness may be reduced. However, the cylindrical lenses may producelight rays that do not contribute to collection of light by a prismsheet and may create another issue that the frontward brightnessdecreases.

As illustrated in FIGS. 7 and 10 to 12, the light exiting surface 19 aof the light guide plate 19 according to this embodiment includes flatportions 45 in addition to the concave lenticular lens portion 44.Furthermore, an occupancy rate of the flat portions 45 with respect tothe second direction varies according to positions with respect to thefirst direction. Specifically, the concave lenticular lens portion 44 isconfigured as follows. A width (or a dimension in the second direction)of the concave cylindrical lens 44 a located close to the light enteringsurface 19 b (or farther from the opposite end surface 19 d) withrespect to the first direction, that is, the occupancy rate with respectto the second direction is higher. The occupancy rate of the concavecylindrical lens 44 a located farther from the light entering surface 19b (or closer to the opposite end surface 19 d) with respect to thesecond direction is lower. The flat portions 45 are flat along the firstdirection (or the X-axis direction) and the second direction (or theY-axis direction). The flat portions 45 are arranged in areas of thelight exiting surface 19 a of the light guide plate 19 in which theconcave lenticular lens portion 44 is not formed. The flat portions 45are arranged adjacent to the concave cylindrical lenses 44 a of theconcave lenticular lens portion 44 with respect to the second direction.The concave cylindrical lenses 44 a and the flat portions 45 arealternately arranged with respect to the second direction on the lightexiting surface 19 a of the light guide plate 19. The widths of the flatportions 45 closer to the light entering surface 19 b (or farther fromthe opposite end surface 19 d) with respect to the first direction aresmaller, that is, the occupancy rates with respect to the seconddirection are lower. The occupancy rates of the flat portions 45 fartherfrom the light entering surface 19 b (or closer to the opposite endsurface 19 d) with respect to the second direction are higher.

More specifically, as illustrated in FIGS. 7 and 10 to 12, the widths ofthe concave cylindrical lenses 44 a, that is, the occupancy rates in thelight exiting surface 19 a with respect to the second directiongradually decrease as a distance from the light entering surface 19 bwith respect to the first direction increases and a distance to theopposite end surface 19 d decreases. The occupancy rates graduallyincrease as the distance from the opposite end surface 19 d with respectto the first direction increases and the distance to the light enteringsurface 19 b decreases. The occupancy rate of the concave cylindricallens 44 a is at a maximum in an end portion (closer to an edge) of thelight guide plate 19 closer to the light entering surface 19 b, which isin a range from 70% to 90%. The occupancy rate of the concavecylindrical lens 44 a is at a minimum in an end portion of the lightguide plate 19 closer to the opposite end surface 19 d, which is in arange from 10% to 30%. The occupancy rate is about 50% in the middleportion of the light guide plate 19 with respect to the first direction.The concave cylindrical lenses 44 a are formed such that heights thereof(or dimensions in the third direction) vary according to positions withrespect to the first direction. Specifically, the concave cylindricallenses 44 a are formed such that the heights, that is, heights from thelight exiting surface 19 a gradually decrease as the distance from thelight entering surface 19 b with respect to the first directionincreases and the distance to the opposite end surface 19 d decreases.The heights gradually increase as the distance from the opposite endsurface 19 d with respect to the first direction increases and thedistance to the light entering surface 19 b decreases. Namely, theheights of the concave cylindrical lenses 44 a vary according to thepositions with respect to the first direction, similarly to the widths.Therefore, surface areas of the concave cylindrical lenses 44 a (areasof the concave surfaces 44 a 1) also vary according to the positionswith respect to the first direction, similarly to the widths and theheights. Each concave cylindrical lens 44 a has a slope that inclines asthe distance from the light entering surface 19 b with respect to thefirst direction increases and the distance to the opposite end surface19 d decreases. The slope declines as the distance from the opposite endsurface 19 d increases and the distance to the light entering surface 19b decreases. Namely, the slope declines toward the light enteringsurface 19 b (toward the LEDs 17). The widths of the flat portions 45,that is, the occupancy rates of the flat portions in the light exitingsurface 19 a with respect to the second direction gradually decrease asthe distance to the light entering surface 19 b with respect to thefirst direction decreases and the distance from the opposite end surface19 d increases. The occupancy rates gradually increase as the distanceto the opposite end surface 19 d with respect to the first directiondecreases and the distance from the light entering surface 19 bincreases. The occupancy rate of the flat portions 45 in the end portion(closer to the edge) of the light guide plate 19 with respect to thefirst direction closer to the light entering surface 19 b is at aminimum, which is in the range from 10% to 30%. The occupancy rate ofthe flat portions 45 in the end portion closer to the opposite endsurface 19 d is at a maximum, which is in the range from 70% to 90%. Theoccupancy rate of the flat portions 45 in the middle portion is about50%. Namely, in the middle area of the light exiting surface 19 a withrespect to the first direction, the occupancy rate of the concavecylindrical lens 44 a with respect to the second direction and theoccupancy rate of the flat portions 45 in the meddle area with respectto the second direction are equal to each other.

As described above, the concave lenticular lens portion 44 adds theanisotropic light collecting effects to the light rays reflected by theexiting light reflecting portion 41. The light rays to which theanisotropic light collecting effects are added are less likely to becollected by the prism sheet 42 with respect to the second direction andmore likely to be diffused with respect to the second direction. Theflat portions 45 arranged adjacent to the concave cylindrical lenses 44a with respect to the second direction are less likely to add specificoptical effects to the light rays reflected by the exiting lightreflecting portion 41. The prism portion 43 dominantly adds theanisotropic light collecting effects to the light rays exiting towardthe prism sheet 42 through the flat portions 45. Therefore, the lightcollecting effects are more likely to be added to the light rays by theprism sheet 42. As the occupancy rate of the concave cylindrical lenses44 a of the concave lenticular lens portion 44 with respect to thesecond direction increases and the occupancy rate of the flat portions45 with respect to the second direction decreases, the uneven brightnessof the light exiting from the prism sheet 42 with respect to the seconddirection is more likely to be reduced. As the occupancy rate of theflat portions 45 with respect to the second direction increases and theoccupancy rate of the concave cylindrical lenses 44 a with respect tothe second direction decreases, the uneven brightness of the lightexiting from the prism sheet 42 is less likely to be reduced but thebrightness tends to increase.

Regarding the concave lenticular lens portion 44 and the flat portions45, as described above, the occupancy rate of the concave lenticularlens portion 44 a with respect to the second direction is higher and theoccupancy rate of the flat portions 45 with respect to the seconddirection is lower in the area closer to the light entering surface 19 bwith respect to the first direction. In the area farther from the lightentering surface 19 b (or closer to the opposite end surface 19 d) withrespect to the first direction, the occupancy rate of the concavecylindrical lenses 44 a with respect to the second direction is lowerand the occupancy rate of the flat portions 45 with respect to thesecond direction is higher. In the area closer to the light enteringsurface 19 b with respect to the first direction in which the unevenbrightness that may be caused by the LEDs 17 arranged along the lightentering surface 19 b may occur, the concave cylindrical lenses 44 a ofthe concave lenticular lens portion 44 with the higher occupancy ratereduce the uneven brightness of the light exiting from the prism sheet42 with respect to the second direction. In the area farther from thelight entering surface 19 b with respect to the first direction in whichthe uneven brightness that may be caused by the LEDs 17 is less likelyto occur, the flat portions 45 with the higher occupancy rate improvethe brightness of the light exiting from the prism sheet 42. Accordingto the configuration, the uneven brightness of the light exiting fromthe prism sheet 42 is reduced and the brightness of the exiting lightimproves.

Comparative experiment 1 was conducted. In comparative experiment 1, alight guide plate that included a light exiting surface, an entire areaof which was configured as a flat portion, and an opposite plate surfaceon which a prism portion was formed was used. Vertex angles of unitprisms of the prism portion were altered and how brightness changed inresponse to the alteration of the vertex angles were determined. Thelight guide plate used in comparative experiment 1 included the flatportion formed on the entire light exiting surface. The light guideplate further included an exiting light reflecting portion and a prismportion formed on the opposite plate surface. The vertex angles of theunit prisms of the prism portion were altered in a range from 90° to160°. The brightness levels of light exiting from the light guide platethrough the light exiting surface, traveling through a prism sheet, andexiting from the prism sheet were measured as the vertex angles werealtered. The results are presented in FIG. 14. The configuration of thelight guide plate used in comparative experiment 1 other than the flatportion formed on the entire light exiting surface is the same as theconfiguration of the light guide plate descried above. The configurationof the prism sheet used in comparative experiment 1 is the same as theconfiguration of the prism sheet described above. In FIG. 14, thehorizontal axis represents vertex angles of the unit prisms (in unit of“°”) and the vertical axis represents relative brightness levels oflight exiting from the prism sheet (in unit of “%”). The relativebrightness levels of the exiting light represented by the vertical axisin FIG. 14 are expressed in brightness levels relative to a reference. Abrightness level of light exiting from the light guide plate(hereinafter referred to as a light guide plate of comparative example2) including the concave lenticular lens portion including the concavecylindrical lenses with a width that did not change for an entire lengthand formed on the entire area of the light exiting surface and the unitprisms of the prism portion on the opposite plate surface with thevertex angle of 100° was defined as the reference (100%). The lightguide plate including the unit prisms with the vertex angle of 100° usedin comparative experiment 1 was referred to as comparative example 1.

The results of comparative experiment 1 will be described. From FIG. 14,when the vertex angles of the unit prisms of the light guide plate usedin comparative experiment 1 were in a range from 90° to 100° or in arange from 120° to 160°, the relative brightness levels were at least 5%higher in comparison to the light guide plate of comparative example 2.When the vertex angles of the unit prisms were in a range from 90° to100° or in a range from 133° to 140°, the relative brightness levelswere at least 10% higher in comparison to the light guide plate ofcomparative example 2. When the vertex angles of the unit prisms were100°, the brightness levels were the highest and the relative brightnesslevels were about 18% higher in comparison to the light guide plate ofcomparative example 2. When the plate portion is formed on the entirelight exiting surface of the light guide plate as in comparativeexperiment 1, specific optical effects are not added to the light by theflat portion. Therefore, the prism portion dominantly adds theanisotropic light collecting effects to the light exiting from the lightguide plate. It is preferable to set the vertex angles of the unitprisms of the prism portion in the range from 90° to 100° or in therange from 120° to 160°, more preferably, in the range from 133° to140°. It is most preferable to set the vertex angles of the unit prismsof the prism portion to 100°. This tendency may be observed in theconfiguration in which the concave lenticular lens portion 44 with thewidth that varies according to the positions with respect to the firstdirection and the flat portions 45 are formed on the light exitingsurface 19 a of the light guide plate.

Comparative experiment 2 was conducted to determine differences inbrightness distribution between a light guide plate including an entirelight exiting surface configured as a flat portion and a light guideplate including an entire light exiting surface configured as alenticular lens portion. In comparative example 2, the light guideplates having the following configurations were used. The light guideplate including the flat portion on the entire light exiting surface andan exiting light reflecting portion and a prism portion including unitprisms with a vertex angle of 100° on an opposite plate surface wasreferred to as comparative example 1. The light guide plate includingthe concave lenticular lens portion including concave cylindrical lenseswith the width that does not change for the entire length with respectto the first direction on the entire light exiting surface and the prismportion including unit prisms with the vertex angle of 100° on theopposite plate surface was referred to as comparative example 2.Brightness distribution of light exiting through the light guide plateof comparative example 1 and a prism sheet and brightness distributionof light exiting through the light guide plate of comparative example 2and a prism sheet were measured. The results are presented in FIG. 15.In FIG. 15, the vertical axis represents relative brightness levels (nounit) of light exiting from the prism sheets and the horizontal axisrepresents angles relative to the frontward direction with respect tothe second direction (in unit of “°”). The relative brightness levelsrepresented by the vertical axis in FIG. 15 are expressed in brightnesslevels relative to a reference. A brightness level relative to thefrontward direction (with the angle of 0°) on the light guide plateaccording to each of comparative examples 1 and 2 is defined as thereference (1.0). In FIG. 15, a solid line expresses measurements ofcomparative example 1 and a broken line expresses measurements ofcomparative example 2. The prism sheet used in comparative experiment 2has the same configuration as the configuration of the prism sheetdescribed above.

Results of comparative experiment 2 will be described. According to FIG.15, the frontward brightness of light exiting from the prism sheet ofcomparative example 1 with respect to the second direction is higherthan the frontward brightness of comparative example 2. Specifically,the light exiting through the light guide plate according to comparativeexample 1 and the prism sheet includes more light rays traveling indirections in an angle range of ±5° relative to the direction toward thefront than the light exiting through the light guide plate according tocomparative example 2 and the prism sheet. Furthermore, the lightexiting through the light guide plate according to comparative example 1and the prism sheet includes less light rays traveling in directions inan angle range of ±5° to ±40° relative to the frontward direction incomparison to the light exiting through the light guide plate accordingto comparative example 2 and the prism sheet. Namely, more light raysexiting through the light guide plate according to the first embodimentand the prism sheet were collected in the frontward direction incomparison to comparative example 2. As illustrated in FIG. 14 accordingto comparative experiment 1, the relative brightness level ofcomparative example 1 including the flat portion on the entire lightexiting surface and the unit prisms with the vertex angle of 100° wasimproved by about 18% from the relative brightness level of comparativeexample 2 including the concave lenticular lens portion on the entirelight exiting surface and the unit prisms with the vertex angle of 100°.

Comparative experiment 3 was conducted to determine whether unevenbrightness occurs in light exiting from light guide plates have thefollowing configurations: a light guide plate including a flat portionin an entire area of a light exiting surface; a light guide plateincluding a concave lenticular lens portion on an entire light exitingsurface; and the light guide plate 19 including the concave lenticularlens portion 44 and the flat portions 45. In comparative experiment 3,the light guide plates according comparative examples 1 and 2 used incomparative experiment 2 described above were used and the light guideplate 19 was used as embodiment 1. The light guide plate 19 according toembodiment 1 includes the concave lenticular lens portion 44 and theflat portions 45. In the area closer to the light entering surface 19 bwith respect to the first direction, the occupancy rate of the concavecylindrical lens 44 a of the concave lenticular lens portion 44 withrespect to the second direction is higher and the occupancy rate of theflat portion with respect to the second direction is lower. In the areafarther from the light entering surface 19 b with respect to the firstdirection, the occupancy rate of the concave cylindrical lens 44 a withrespect to the second direction is lower and the occupancy rate of theflat portions 45 with respect to the second direction is higher. Thedetailed configuration is the same as the configuration of the lightguide plate described before the description of comparativeexperiment 1. The vertex angle θv2 of the unit prisms 43 a of the prismportion 43 on the opposite plate surface 19 c of the light guide plate19 according to embodiment 1 is 100°. In comparative experiment 3, inthe backlight units including the light guide plates according tocomparative examples 1 and 2 and embodiment 1, respectively, pictureswere taken from the light exiting surface side in a condition that thelight from the LEDs enters the light guide plates through the lightentering surfaces and exit from the light exiting surfaces to determinewhether uneven brightness was present based on the pictures. The resultsare presented in FIG. 16. Each of the backlight units has aconfiguration the same as the configuration of the backlight unitdescribed before the description of comparative experiment 1 except foreach of the light guide plates according to comparative examples 1 and 2and embodiment 1. The pictures taken from the light exiting surface sidein the condition that the light exiting from the light guide platesthrough the light exiting surfaces according to the comparative examples1 and 2 and embodiment 1 and the results of the determination about theuneven brightness based on the pictures are presented in FIG. 16. Thepictures in FIG. 16 include portions of the light exiting surfaces ofthe light guide plates. The LEDs are arranged on below lower ends of thelight guide plates in FIG. 16.

Results of comparative experiment 3 will be described. In FIG. 16, theuneven brightness is observed in the picture of the light guide plateaccording to comparative example 1 but the uneven brightness is rarelyobserved in the picture of the light guide plate according tocomparative example 2. The light guide plate according to comparativeexample 1 included the entire light exiting surface configured as theflat portion and did not include the concave lenticular lens portion.Therefore, light traveling through the light guide plate was diffusedwith respect to the second direction at a lower level. As a result, theuneven brightness occurred in the light exiting from the light exitingsurface such that bright spots and dark spots alternately appeared withrespect to the second direction (or the arrangement direction of theLEDs). Contrarily, the light guide plates according to comparativeexample 2 and embodiment 1 had the configurations in which the concavelenticular lens portions were formed on the light exiting surfaces. Thelight traveling each of the light guide plates was properly diffused bythe concave lenticular lens portion with respect to the seconddirection. Therefore, the uneven brightness with respect to the seconddirection rarely occurred in the light exiting from the light exitingsurface. There was not much difference in level of uneven brightnessbetween the comparative example 2 and embodiment 1. In comparison tocomparative example 2, the occupancy rate of the concave lenticular lensportion 44 in the light exiting surface 19 a in embodiment 1 was lower.However, in the area of the light exiting surface 19 a closer to thelight entering surface 19 b in which the uneven brightness may occur dueto arrangement of the LEDs 17 (in which the LEDs 17 were arranged atintervals along the light entering surface 19 b), the widths of theconcave cylindrical lenses 44 a of the concave lenticular lens portion44 were sufficiently large, that is, the occupancy rate of the concavecylindrical lenses 44 a was sufficiently high. Therefore, in the areacloser to the light entering surface 19 b with respect to the firstdirection, the light traveling through the light guide plate 19 wasdiffused with respect to the second direction at a sufficient level bythe concave lenticular lens portion 44. As a result, the unevenbrightness with respect to the second direction was reduced at the samelevel as comparative sample 2.

Comparative experiment 4 was conducted to determine differences inbrightness distribution between a configuration in which a concavelenticular lens portion including concave cylindrical lenses having awidth that did not change for an entire length was formed on an entirelight exiting surface and a configuration in which the concavelenticular lens portion 44 with the occupancy rate with respect to thesecond direction which changed according to the positions with respectto the first direction and the flat portions 45 on the light exitingsurface 19 a. In comparative experiment 4, the light guide plateaccording to comparative example 2 in the description of comparativeexperiment 2 and the light guide plate 19 according to embodiment 1 inthe description of comparative experiment 3 were used. Brightnessdistributions of light exiting through the light guide plate accordingto comparative example 2 and the prism sheet and light exiting throughthe light guide plate according to embodiment 1 and the prism sheet weremeasured. The measurements are presented in FIGS. 17 to 19. Themeasurements of the brightness distributions were performed at threepoints of each of the light guide plate according to comparative example2 and embodiment 1: a point closer to the light entering surface withrespect to the first direction; a point in the middle; and a pointcloser to the opposite plate surface. The measurements at the pointcloser to the light entering surface are present in FIG. 17. Themeasurements at the point in the middle are presented in FIG. 18. Themeasurements at the point closer to the opposite plate surface arepresented in FIG. 19. In each of FIGS. 17 to 19, the vertical axisrepresents relative brightness levels (no unit) of light exiting fromthe prism sheet and the horizontal axis represents angle relative to thefrontward direction with respect to the second direction (in unit of“°”). The relative brightness levels represented by the vertical axis ineach of FIGS. 17 to 19 are expressed in brightness levels relative to areference. A brightness level relative to the frontward direction (withthe angle of 0°) on the light guide plate according to each ofcomparative example 2 and embodiment 1 was defined as the reference(1.0). In each of FIGS. 17 to 19, a broken line expresses themeasurements of comparative example 2 and a solid line expresses themeasurements of embodiment 1. Each prism sheet used in comparativeexperiment 4 had the same configuration as the configuration of theprism sheet in the description before this paragraph.

Results of comparative experiment 4 will be described. In FIGS. 17 to19, the frontward brightness of the light guide plate 19 according toembodiment 1 is higher at any point with respect to the first directionin comparison to the light guide plate according to comparativeexample 1. From comparison between FIGS. 18 and 19, it is obvious thatthe front brightness of embodiment 1 is higher at the point closer tothe opposite end surface with respect to the first direction than at thepoint in the middle with respect to the first direction. The frontwardbrightness of the light guide plate 19 according to embodiment 1increased as the distance from the light entering surface 19 b increasedand the distance to the opposite end surface 19 d decreased. Thisexpresses tendency that the front brightness is inversely proportionalto variations in width of the concave cylindrical lenses 44 a. The widthof the concave cylindrical lenses 44 a (or the occupancy rate thereofwith respect to the second direction) was at a maximum at an endposition closer to the light entering surface 19 b with respect to thefirst direction and at a minimum at an end position closer to theopposite end surface 19 d with respect to the first direction. As thewidth decreased, the frontward brightness of the light exiting throughthe light guide plate 19 and the prism sheet 42 improved. The concavecylindrical lenses 44 a having the width that varied as above properlyreduced the uneven brightness with respect to the second direction withthe width set larger in the area closer to the light entering surface 19b with respect to the first direction. Furthermore, in the middle areaor the area closer to the opposite end surface 19 d with respect to thefirst direction in which such uneven brightness was less likely tooccur, the concave cylindrical lenses 44 a having a smaller widthimproved the frontward brightness achieved with the light exiting fromthe prism sheet. The brightness level of the light exiting through thelight guide plate 19 according to embodiment 1 and the prism sheet 42was measured. The brightness level was improved by about 9% incomparison to the brightness level of the light exiting through thelight guide plate according to comparative example 2.

A relationship between the exiting light reflecting portion 41 and theprism portion 43 on the opposite plate surface 19 c of the light guideplate 19 will be described in detail. As illustrated in FIGS. 7 and 10,the unit reflectors 41 a of the exiting light reflecting portion 41 areformed by cutting portions of the unit prisms 43 a of the prism portion43 on the vertex 43 a 2 side. The unit reflectors 41 a are not formed bycutting portions of the bottoms of the unit prisms 43 a on the oppositeside from the vertex 43 a 2 side, that is, the bottoms are non-formingportions in which the unit reflectors 41 a are not formed. The height ofthe unit reflectors 41 a (or the dimension in the third direction) issmaller than the height of the unit prisms 43 a. According to theconfiguration, as illustrated in FIG. 7, the unit reflectors 41 a extendalong the second direction but do not continuously extend for the entirelength of the light guide plate 19 with respect to the second directionand have breaks. In other words, the unit reflectors 41 a includesegment unit reflectors 41 aS that are arranged at intervals withrespect to the second direction. Furthermore, the unit reflectors 41 aare formed by cutting portions of the unit prisms 43 a on the vertex 43a 2 side such that the unit reflectors 41 a open toward sides along thesecond direction. The number of the segment unit reflectors 41 aS of theunit reflectors 41 a is equal to a total number of the unit prisms 43 aof the prism portion 43. A middle point of each unit reflector 41 a withrespect to the second direction substantially corresponds with thelocation of the vertex 43 a 2 of the corresponding unit prism 43 a withrespect to the second direction. The height (or the depth) of each ofthe unit reflectors 41 a arranged with respect to the first directiongradually increases as the distance from the light entering surface (ofthe LEDs 17) with respect to the first direction increases (see FIG. 3).The width of the unit reflector 41 a (or the area in which the unitreflector 41 a is formed with respect to the second direction) graduallyincreases as the distance from the light entering surface 19 b withrespect to the first direction increases. As illustrated in FIG. 8, thewidth of the unit reflectors 41 a arranged closer to the light enteringsurface 19 b with respect to the first direction is smaller and thesurface area thereof is smaller. The width of the unit reflectors 41 acloser to the opposite end surface 19 d with respect to the firstdirection is larger and the surface area of the unit reflectors 41 a islarger.

The amount of reflected light tends to be proportional to the surfacearea of the unit reflectors 41 a described above. To achieve a necessaryamount of reflected light, the surface area needs to correspond to thenecessary amount of reflected light. This applies to the exiting lightreflecting portion 41. To achieve the necessary amount of reflectedlight by the exiting light reflecting portion 41, a total surface areaof the exiting light reflecting portion 41 (or a total area includingthe surface area of the unit reflectors 41 a) needs to correspond to thenecessary amount. If the unit reflectors are formed to extend for theentire length of the light guide plate 19 in the second direction, thedimensions of the unit reflectors in the third direction cannot beincreased more than specific dimensions. The unit reflectors 41 ainclude the segment unit reflectors 41 aS that are arranged at intervalswith respect to the second direction. To set the surface area of theunit reflectors 41 a as described above, the dimensions of the unitreflectors 41 a in the third direction can be increased. In thepreparation of the light guide plate 19 by molding in which the exitinglight reflecting portion 41 is integrally formed with the opposite platesurface 19 c, the segment unit reflectors 41 aS of the unit reflectors41 a can be easily formed in designed shapes in the opposite platesurface 19 c. Therefore, the exiting light reflecting portion 41 canproperly deliver the optical performances. If the unit reflectors areformed to extend for the entire length of the light guide plate 19 withrespect to the second direction, the number of the unit reflectorsarranged with respect to the first direction may be reduced. Accordingto the configuration, the total surface area including the surface areasof the unit reflectors may be adjusted. However, the intervals betweenthe unit reflectors with respect to the first direction increase andthus the uneven brightness may occur. Because the unit reflectors 41 ainclude the segment unit reflectors 41 aS arranged at intervals withrespect to the second direction, the number and the intervals of theunit reflectors 41 a with respect to the first direction do not need tobe altered. Therefore, the uneven brightness is less likely to occur inlight exiting from the backlight unit 12. Furthermore, the unitreflectors 41 a are formed by cutting the portions of the unit prisms 43a on the vertex 43 a 2 side to open along the second direction.According to the configuration, the prism portion 43 can properlydeliver the light collecting performances. If the unit reflectors do notopen along the second direction and have side surfaces along the firstdirection, light rays may be refracted at or reflected by the sidesurfaces along the first direction. Namely, the prisms may not deliverproper levels of light collecting performances. Because the unitreflectors 41 a are formed by cutting the portions of the unit prisms 43a on the vertex 43 a 2 side to open along the second direction, theprism portion 43 can properly deliver the light collecting performances.According to the configuration, the brightness of the light exiting fromthe backlight unit can be further increased.

Comparative experiment 5 was conducted to determine how shapereproducibility of the unit reflectors 41 a of the exiting lightreflecting portion 41 changed between the configurations with andwithout the prism portion 43. In comparative experiment 5, the lightguide plate 19 including the exiting light reflecting portion 41 and theprism portion 43 on the opposite plate surface 19 c was referred asembodiment 1 and a light guide plate including the exiting lightreflecting portions formed on the opposite plate surface but not theprism portions was referred to as comparative example 3. Theconfiguration of the light guide plate according to comparative example3 in comparative experiment 5 other than the prism portions that werenot included was the same as the configuration of the light guide plate19 according to embodiment 1. Unit reflectors on the light guide plateaccording to comparative example 3 were formed to continuously extendfor the entire length of the light guide plate with respect to thesecond direction (or the Y-axis direction). The number of the unitreflectors with respect to the first direction (or the X-axis direction)was equal to the number of the unit reflectors 41 a on the light guideplate 19 according to embodiment 1. In comparative experiment 5, heightsof the unit reflectors of the light guide plate according to comparativeexample 3 and the light guide plate 19 according embodiment 1 weremeasured. Results are presented in FIG. 20. The unit reflectors wereincluded in the light reflecting portions corresponding to positionswith respect to the first direction. In comparative experiment 5, eachof the light guide plates according to comparative example 3 andembodiment 1 was divided substantially equally into 6 sections withrespect to the first direction. Boundaries of the sections were referredto as a first position, a second position, a third position, a fourthposition, and a fifth position from the side closer to the lightentering surface. The shape reproducibility of the unit reflectors 41 awas determined for each position. Results are presented in FIG. 21. InFIG. 20, the vertical axis represents height of the unit reflectors (inunit of “μm”) and the horizontal axis represents position on each lightguide plate with respect to the first direction. The leftmost positionon the horizontal axis with respect to the first direction in FIG. 20corresponds to the light entering surface of each light guide plate. Therightmost position in FIG. 20 corresponds to the opposite end surface ofeach light guide plate. In FIG. 21, the heights of the unit reflectorsat the first to the fifth positions and results of evaluation of theshape reproducibility of the unit reflectors are present. The shapereproducibility of the unit reflectors was evaluated based ondifferences between light distributions (theoretical values) regardinglight exiting from a light guide plate defined in optical simulation anda light distribution (measurements) regarding the light guide platesactually produced by molding. If the differences were out of thetolerance, the shape reproducibility was determined as “bad.” If thedifferences were within the tolerance, the shape reproducibility wasdetermined as “good.”

Results of comparative experiment 5 will be described. FIG. 20 describesthat the light guide plate 19 according to embodiment 1 and the lightguide plate according to comparative example 3 have heights thatgradually increase from the light entering surface side to the oppositesurface side. FIG. 20 also describes that the unit reflectors 41 a onthe light guide plate 19 according to embodiment 1 have heights largerthan those of the unit reflectors on the light guide plate according tocomparative example 3. This results from the fact that the unitreflectors on the light guide plate according to comparative example 3continuously extend for the entire length of the light guide plate withrespect to the second direction but the unit reflectors 41 a on thelight guide plate 19 according to embodiment 1 include the segment unitreflectors 41 aS arranged at intervals with respect to the seconddirection. The reason will be described in detail below. The surfacearea of the unit reflectors and the amount of the light reflected by theunit reflectors are proportional to each other. To achieve the necessaryamount of the reflected light, the surface area of the unit reflectorsneeds to be set to correspond to the target amount of the reflectedlight. The unit reflectors on the light guide plate according tocomparative example 3 continuously extend for the entire length of thelight guide plate with respect to the second direction. Therefore, theheights of the unit reflectors cannot be significantly increased to setthe surface area of the unit reflectors as described above. The unitreflectors 41 a on the light guide plate according to embodiment 1include the segment unit reflectors 41 aS arranged at intervals withrespect to the second direction. The heights of the unit reflectors 41 acan be increased in comparison to comparative example 3 to set thesurface area of the unit reflectors 41 a. For such a reason, the unitreflectors 41 a on the light guide plate 19 according to embodiment 1have the heights larger than those of the unit reflectors on the lightguide plate according to comparative example 3.

FIG. 21 describes that the unit reflectors exert good shapereproducibility when the heights of the unit reflectors are about 3 μmor larger. At the first to the fourth positions, the shapereproducibility of the unit reflectors on the light guide plateaccording to comparative example 3 was determined as bad. At the fifthposition, the shape reproducibility was determined as reasonably good.This was because the heights of the most unit reflectors on the lightguide plate according to comparative example 2 were less than thereference (3 μm) while the heights of the most unit reflectors 41 a onthe light guide plate 19 according to embodiment 1 were larger than 3μm, which was the reference for determination of the shapereproducibility of the unit reflectors. As described above, inembodiment 1, the prism portion 43 is formed on the opposite platesurface 19 c of the light guide plate 19 in addition to the exitinglight reflecting portion 41 and the unit reflectors 41 a of the exitinglight reflecting portion 41 include the segment unit reflectors 41 aS.According to the configuration, the unit reflectors 41 a can be formedwith the sufficiently large heights. Therefore, in the production of thelight guide plate 19 by molding, the segment unit reflectors 41 aS ofthe unit reflectors 41 a can be easily formed in designed shapes. Thisallows the exiting light reflecting portion 41 properly deliver theoptical performances. To increase the heights of the unit reflectors onthe light guide plate according to comparative example 3, the number ofthe unit reflectors with respect to the first direction may be reducedto adjust the total of the surface areas of the unit reflectors to aspecific value. If the number is reduced, the intervals of the unitreflector with respect to the first direction increase and thus unevenbrightness may occur in light exiting from the light guide plate.Because the unit reflectors 41 a on the light guide plate according toembodiment 1 include the segment unit reflectors 41 aS arranged atintervals with respect to the second direction, the number and theintervals of the unit reflectors 41 a with respect to the firstdirection do not need to be altered, the uneven brightness is lesslikely to occur in the light exiting from the light guide plate 19.

As described above, the backlight unit (the lighting device) 12according to this embodiment includes the LEDs (the light sources) 17,the light guide plate 19, the exiting light reflecting portion 41, theprism sheet (the light exiting-side anisotropic light collectingportion) 42, the prism portion 43, the concave lenticular lens portion(the lenticular lens portion) 44, and the flat portions 45. The lightguide plate 19 has a rectangular plate shape including a pair of endsurfaces, at least one of which is configured as the light enteringsurface 19 b through which the light emitted by the LEDs 17 enters. Thelight guide plate 19 further includes the plate surfaces, one of whichis configured as the light exiting surface 19 a through which the lightexits and the other one of which is configured as the opposite platesurface 19 c. The prism sheet 42 includes the light exiting-side unitprisms (the light exiting-side unit collecting portions) 42 a thatextend along the first direction along the pair of end surfaces of thelight guide plate which do not include the light entering surface 19 band opposite to each other. The light exiting-side unit prisms 42 a arearranged along the second direction along the pair of end surfaces ofthe light guide plate 19 which include the light entering surface 19 b.The exiting light reflecting portions 41 are arranged on one of thelight exiting surface 19 a and the opposite plate surface 19 c of thelight guide plate for reflecting the light rays traveling through thelight guide plate 19 and directing the light rays to exit through thelight exiting surface 19 a. The exiting light reflecting portions 41include the unit reflectors 41 a that extend along the second directionand lines of which are arranged at intervals along the first direction.The prism portion 43 is formed on one of the light exiting surface 19 aside and the opposite plate surface 19 c side of the light guide plate19. The prism portion 43 includes the unit prisms 43 a that extend alongthe first direction. The unit prisms 43 a are arranged along the seconddirection. The concave lenticular lens portion 44 is formed in the otherone of the light exiting surface 19 a and the opposite plate surface 19c of the light guide plate 19. The concave lenticular lens portion 44includes the concave cylindrical lenses (the cylindrical lenses) 44 athat extend along the first direction. The concave cylindrical lenses 44a are arranged along the second direction. The occupancy rate of theconcave cylindrical lenses 44 a with respect to the second direction ishigher in the area closer to the light entering surface 19 b withrespect to the first direction. The occupancy rate of the concavecylindrical lenses 44 a with respect to the second direction is lower inthe area farther from the light entering surface 19 b. The flat portions45 are formed on the other one of the light exiting surface 19 a and theopposite plate surface 19 c. The flat portions 45 are flat along thefirst direction and the second direction. The flat portions 45 areadjacent to the concave cylindrical lenses 44 a with respect to thesecond direction. The occupancy rate of the flat portions 45 withrespect to the second direction is lower in the area closer to the lightentering surface 19 b with respect to the first direction. The occupancyrate with respect to the second direction is higher in the area fartherfrom the light entering surface 19 b.

According to the configuration, the light rays emitted by the LEDs 17enter the light guide plate 19 through the light entering surface 19 band travel through the light guide plate 19. While traveling through thelight guide plate 19, the light rays are reflected by the exiting lightreflecting portion 41. The unit reflectors 41 a of the exiting lightreflecting portion 41 extend along the second direction and lines of theunit reflectors 41 a are arranged at intervals along the firstdirection. Therefore, the unit reflectors 41 a can reflect the lightrays traveling along the first direction through the light guide plate19 and direct the light rays to exit from the light exiting surface 19a. The anisotropic light collecting effects are added to at least somelight rays exiting from the light exiting surface 19 a by at least oneof the prism portion 43 and the concave lenticular lens portion 44. Theprism portion 43 and the concave lenticular lens portion 44 include theunit prisms 43 a and the concave cylindrical lenses 44 a, respectively.The prism portion 43 and the concave lenticular lens portion 44 extendalong the first direction. The prism portion 43 and the concavelenticular lens portion 44 are arranged along the second direction.According to the configuration, the light collecting effects areselectively added to at least some of light rays exiting from the lightexiting surface 19 a by at least one of the unit prisms 43 a and theconcave cylindrical lenses 44 a with respect to the second direction.

The light rays that travel along the first direction through the lightguide plate 19 without being reflected by the exiting light reflectingportion 41 are totally reflected by the prism portion 43 and the concavelenticular lens portion 44. As a result, the light rays are diffusedwith respect to the second direction and transmitted through the lightguide plate 19. Because the concave lenticular lens portion 44 includesthe concave cylindrical lenses 44 a, the light rays that are totallyreflected by the concave cylindrical lenses 44 a are diffused in thewider area with respect to the second direction.

The anisotropic light collecting effects are added to the light raysexiting from the light guide plate 19 through the light exiting surface19 a by the prism sheet 42 on the light exiting side with respect to thelight guide plate 19. The prism sheet 42 includes the light exiting-sideunit prisms 42 a that extend along the first direction. The lightexiting-side unit prisms 42 a are arranged along the second direction.According to the configuration, the light collecting effects areselectively added to the light rays exiting from the light exiting-sideunit prisms 42 a with respect to the second direction in which the lightexiting-side unit prisms 42 a are arranged. The concave cylindricallenses 44 a of the concave lenticular lens portion 44 add theanisotropic light collecting effects to the light rays reflected by theexiting light reflecting portion 41 as described above. However, thelight rays to which the anisotropic light collecting effects are addedare less likely to be collected by the prism sheet 42 with respect tothe second direction and more likely to be diffused with respect to thesecond direction. The flat portions 45 adjacent to the concavecylindrical lenses 44 a with respect to the second direction are lesslikely to add specific optical effects to the light rays reflected bythe exiting light reflecting portion 41. Therefore, the anisotropiclight collecting effects are dominantly added to the light rays directedto the prism sheet 42 via the flat portions 45 by the prism portion 43and thus the light collecting effects are more likely to be added by theprism sheet 42 with respect to the second direction. As the occupancyrate of the concave cylindrical lenses 44 a of the concave lenticularlens portion 44 with respect to the second direction increases and theoccupancy rate of the flat portions 45 with respect to the seconddirection decreases, the uneven brightness of the light exiting from theprism sheet 42 with respect to the second direction is more likely to bereduced but the brightness is more likely to be decreased. As theoccupancy rate of the flat portions 45 with respect to the seconddirection increases and the occupancy rate of the concave cylindricallenses 44 a with respect to the second direction decreases, the unevenbrightness of the light exiting from the prism sheet 42 is less likelyto be reduced but the brightness is more likely to be increased.

As described above, in the area closer to the light entering surface 19b with respect to the first direction, the occupancy rate of the concavecylindrical lenses 44 a of the concave lenticular lens portion 44 withrespect to the second direction is higher and the occupancy rate of theflat portions 45 with respect to the second direction is lower. In thearea farther from the light entering surface 19 b with respect to thefirst direction, the occupancy rate of the concave cylindrical lenses 44a with respect to the second direction is lower and the occupancy rateof the flat portions 45 with respect to the second direction is higher.In the area closer to the light entering surface 19 b with respect tothe first direction in which the uneven brightness resulting from theLEDs 17 are more likely to occur, with the concave cylindrical lenses 44a of the concave lenticular lens portion 44 having the higher occupancyrate, the uneven brightness is less likely to occur in the light exitingfrom the prism sheet 42 with respect to the second direction. In thearea farther from the light entering surface 19 b with respect to thefirst direction in which the uneven brightness resulting from the LEDs17 is less likely to occur, with the flat portions 45 having the higheroccupancy rate, the higher brightness is achieved for the light exitingfrom the prism sheet 42.

The exiting light reflecting portions 41 and the prism portion 43 areformed on the opposite plate surface 19 c side of the light guide plate19. The concave lenticular lens portion 44 is formed on the lightexiting surface 19 a side of the light guide plate 19. According to theconfiguration, some of the light rays reflected by the unit reflectors41 a of the exiting light reflecting portion 41 on the opposite platesurface 19 c side of the light guide plate 19, to which the anisotropiclight collecting effects are added by the prism portion 43, are directedto the light exiting surface 19 a. The anisotropic light collectingeffects are added to the light rays that have reached the light exitingsurface 19 a by the concave lenticular lens portion 44 that is formed onthe light exiting surface 19 a. In comparison to a configuration inwhich the exiting light reflecting portions on the light exiting surface19 a side, a light path through which the light rays reflected by theexiting light reflecting portion 41 travels before exiting from thelight exiting surface 19 a is simpler and losses of the light rays areless likely to occur. Therefore, a decrease in brightness is less likelyto occur.

The vertex angle θv2 of each unit prism 43 a of the prism portion 43 maybe in the range from 90° to 100°. In comparison to the configuration inwhich the occupancy rate of the concave cylindrical lenses with respectto the second direction is constant, the brightness of the light exitingfrom the light exiting surface 19 a can be sufficiently improved.

The vertex angle θv2 of each unit prism 43 a of the prism portion 43 maybe 100°. In comparison to the configuration in which the occupancy rateof the concave cylindrical lenses with respect to the second directionis constant, the brightness of the light exiting from the light exitingsurface 19 a can be improved more than others.

The vertex angle θv2 of each unit prism 43 a of the prism portion 43 maybe in the range from 120° to 160°. In comparison to the configuration inwhich the occupancy rate of the concave cylindrical lenses with respectto the second direction is constant, the brightness of the light exitingfrom the light exiting surface 19 a can be sufficiently improved.

The vertex angle θv2 of each unit prism 43 a of the prism portion 43 maybe in the range from 133° to 140°. In comparison to the configuration inwhich the occupancy rate of the concave cylindrical lenses with respectto the second direction is constant, the brightness of the light exitingfrom the light exiting surface 19 a can be more improved.

The concave lenticular lens portion 44 includes the concave cylindricallenses 44 a each having recessed shapes. In comparison to aconfiguration in which the cylindrical lenses have protruding shapes,the light rays traveling through the light guide plate 19 are morelikely to enter the interfaces that are curved surfaces of the concavecylindrical lenses 44 a with the angles of incidence larger than thecritical angle. Therefore, the light rays are less likely to exitthrough the interfaces. The light rays traveling through the light guideplate 19 are more likely to be totally reflected by the concavecylindrical lenses 44 a and to be diffused with respect to the seconddirection. Therefore, the uneven brightness is further less likely tooccur with respect to the second direction.

The occupancy rate of the concave cylindrical lenses 44 a of the concavelenticular lens portion 44 with respect to the second directiongradually and continuously decreases as the distance from the lightentering surface 19 b with respect to the first direction increases. Theoccupancy rate of the flat portions 45 with respect to the seconddirection gradually and continuously increases as the distance from thelight entering surface 19 b with respect to the first directionincreases. In comparison to a configuration in which the occupancy rateof the concave cylindrical lenses of the concave lenticular lens portionwith respect to the second direction and the occupancy rate of the flatportions with respect to the second direction are altered in steps, theuneven brightness is more properly reduced and the brightness isproperly improved.

The unit reflectors 41 a of the exiting light reflecting portion 41include the segment unit reflectors 41 aS arranged at intervals withrespect to the second direction. The amount of light reflected by theunit reflectors 41 a tends to be proportional to the surface area of theunit reflectors 41 a. To achieve the necessary amount of the reflectedlight, the surface area need to be set corresponding to the necessaryamount. If the unit reflectors are formed to extend for the entirelength of the light guide plate 19 with respect to the second direction,dimensions of the unit reflectors 41 a in the direction normal to theplate surface of the light guide plate 19 cannot be increased more thana certain dimension to set the surface area of the unit reflectors 41 aas described above. According to the configuration in which the unitreflectors 41 a include the segment unit reflectors 41 aS that arearranged at intervals with respect to the second direction, thedimensions of the unit reflectors 41 a in the direction normal to theplate surface of the light guide plate 19 can be increased to set thesurface area of the unit reflectors 41 a as described above. In theproduction of the light guide plate 19 by molding in which the exitinglight reflecting portion 41 are integrally formed with one of the lightexiting surface 19 a and the opposite plate surface 19 c, the segmentunit reflectors 41 aS of the unit reflectors 41 a can be easily formedin the designed shape in the one of the light exiting surface 19 a andthe opposite plate surface 19 c. According to the configuration, theexiting light reflecting portion 41 can properly deliver the opticalperformances.

If the unit reflectors are formed to extend for the entire length of thelight guide plate 19 with respect to the second direction, the number oflines of the unit reflectors 41 a in the first direction may be reducedto adjust the total area of the unit reflectors 41 a, which is the sumof the surface areas of the unit reflectors 41 a. However, by reducingthe number, the intervals of the lines of the unit reflectors 41 aarranged in the first direction increase. This may cause the unevenbrightness. Because the unit reflectors 41 a include the segment unitreflectors 41 aS arranged at intervals with respect to the seconddirection, the number and the intervals of the lines of the unitreflectors 41 a arranged in the first direction do not need to bealtered. Therefore, the uneven brightness is less likely to occur in thelight exiting from the backlight unit 12.

The unit reflectors 41 a of the exiting light reflecting portion 41 areformed by cutting portions of the unit prisms 43 a of the prism portion43 on the vertex 43 a 2 side to open along the second direction. Incomparison to a configuration in which the unit reflectors 41 a do notopen along the second direction and cover the side surfaces along thefirst direction, light rays may be refracted at or the reflected by theside surfaces along the first direction. Namely, the prism portion 43may not deliver proper levels of light collecting performances. Becausethe exiting light reflecting portion 41 are formed such that the unitreflectors 41 a are formed by the portions of the unit prisms 43 a onthe vertex 43 a 2 side to open along the second direction, the prismportion 43 can properly deliver the light collecting performances andthus the brightness related to the light exiting from the backlight unit12 further improves.

The liquid crystal display device (the display device) 10 according tothis embodiment includes the backlight unit 12 described above and theliquid crystal panel (the display panel) 11 for displaying images usingthe light from the backlight unit 12. According to the liquid crystaldisplay device 10 having such a configuration, the uneven brightness isless likely to occur in the light exiting from the backlight unit 12 andthe high brightness is achieved. Therefore, high display quality isachieved.

Second Embodiment

A second embodiment of the present invention will be described withreference to FIGS. 22 to 31. The second embodiment includes exitinglight reflecting portions 141, a prism portion 143, a concave lenticularlens portion 144, and flat portions 145 arranged inversely to the firstembodiment. Configurations, functions, and effects similar to those ofthe first embodiment described above will not be described.

As illustrated in FIGS. 22 to 24, a light guide plate 119 according tothis embodiment includes the exiting light reflecting portions 141 andthe prism portion 143 on a light exiting surface 119 a side and theconcave lenticular lens portion (opposite plate surface-side lenticularlens portion) 144 and the flat portions 145 on an opposite plate surface119 c side. Structures on the surfaces 119 a and 119 c are arrangedinversely to the structures on the plate surfaces 19 a and 19 c of thelight guide plate according to the first embodiment described above. Theprism portion 143, the concave lenticular lens portion 144, and the flatportions 145 on the light guide plate 119 have configurations similar tothose of the first embodiment described above except for thearrangements on the plate surfaces 119 a and 119 c of the light guideplate 119. As illustrated in FIGS. 22 and 24 to 26, occupancy rates ofthe concave lenticular lens portion 144 and the flat portions 145 withrespect to the second direction in the opposite plate surface 119 c varyaccording to positions with respect to the first direction. In an areacloser to a light entering surface 119 b with respect to the firstdirection, the occupancy rate of the concave cylindrical lenses(opposite plate surface-side cylindrical lenses) 144 a is higher and theoccupancy rate of the flat portions 145 is lower. In an area fartherfrom the light entering surface 119 b (or closer to an opposite endsurface 119 d), the occupancy rate of the concave cylindrical lenses 144a is lower and the occupancy rate of the flat portions 145 is higher.

As illustrated in FIG. 24, predefined clearances C1 are provided betweenthe concave cylindrical lenses 144 a of the concave lenticular lensportion 144 on the opposite plate surface 119 c side of the light guideplate 119 and a reflection sheet 140. The clearances C1 are air layersbetween the opposite plate surface 119 c of the light guide plate 119and the reflection sheet 140 and each having a refractive index of 1.0.Each clearance C1 has a height (or a dimension in the third direction)which varies according to positions with respect to the second direction(or the X-axis direction). Specifically, the height decreases as adistance from the middle of the concave cylindrical lens 144 a towardeither end with respect to the second direction increases. A variationin height depends on a curvature of the concave cylindrical lens 144 a.As illustrated in FIGS. 24 to 26, each clearance C1 has a height thatvaries according to positions with respect to the first direction (orthe Y-axis direction). Specifically, the height decreases as a distancefrom the light entering surface 119 b toward the opposite end surfacewith respect to the first direction increases. A variation in height isequal to the variation in height of the concave cylindrical lens 144 a.The flat portions 145 are adjacent to a reflecting surface 140 a of thereflection sheet 140.

This embodiment includes the exiting light reflecting portions 141 onthe light exiting surface 119 a side of the light guide plate 119.Therefore, this embodiment has the following function. Light rays enterthe light guide plate 119 through the light entering surface 119 b andtravel toward the opposite end surface 119 d through the light guideplate 119 along the first direction. When the light rays reach the lightexiting surface 119 a, some of the light rays may be reflected by theexiting light reflecting portions 141 and directed to the opposite platesurface 119 c. After the light rays reflected by the exiting lightreflecting portions 141 reach the opposite plate surface 119 c, thelight rays may enter concave surfaces 144 a 1 with angles smaller thanthe critical angle. If the light rays enter the concave surfaces 144 a 1with the angles smaller than the critical angle, the light rays may berefracted at the concave surfaces 144 a 1 and directed to the clearancesC1 between the concave surfaces 144 a 1 and the reflection sheet 140.The light rays directed to the clearances C1 are reflected off areflecting surface 140 a of the reflection sheet 140. After reached theopposite plate surface 119 c again, the light rays reflected off thereflecting surface 140 a of the reflection sheet 140 enter the concavesurfaces 144 a 1 of the concave cylindrical lenses 144 a. The light raysare refracted at the concave surfaces 144 a 1 and directed to the lightexiting surface 19 a. Every time when the light rays enter the oppositeplate surface 119 c and exit from the opposite plate surface 119 c viathe clearances C1, anisotropic light collecting effects are added to thelight rays by the concave cylindrical lenses 144 a. Namely, lightcollecting effects with respect to the second direction are selectivelyadded to the light rays by the concave cylindrical lenses 144 a. Opticaleffects for diffusing the light rays with respect to the seconddirection are added to the light rays to which the anisotropic lightcollecting effects are not added every time when time when the lightrays enter the opposite plate surface 119 c and exit from the oppositeplate surface 119 c. The light rays to which the anisotropic lightcollecting effects are not added by the concave cylindrical lenses 144 aare refracted twice when entering and exiting through the opposite platesurface 119 c. As a result, the light rays are diffused in a wide areawith respect to the second direction and the light rays are properlymixed with respect to the second direction. According to theconfiguration, the uneven brightness is less likely to occur in lightexiting from the light exiting surface 119 a with respect to the seconddirection. The light rays to which the anisotropic light collectingeffects are added by the concave cylindrical lenses 144 a are lesslikely to be collected by a prism sheet 142 with respect to the seconddirection but more likely to be diffused with respect to the seconddirection. Therefore, the light rays may improve the uneven brightnessrelated to the light exiting from the prism sheet 142 but may notcontribute to improvement of the frontward brightness.

Comparative experiment 6 was performed to determine differences inbrightness distribution of light exiting from a prism sheet between alight guide plate including a flat portion formed in an entire area ofan opposite plate surface and a light guide plate including concavelenticular lens portion formed in an entire area of an opposite platesurface. Each of the light guide plates includes exiting lightreflecting portions and a prism portion on a light exiting side andconcave lenticular lens portion on an opposite plate surface side. Incomparative experiment 6, the following light guide plates were used.The light guide plate including the flat portion in the entire area ofthe opposite plate surface was referred to as comparative example 4. Thelight guide plate including the concave lenticular lens portion in theentire area of the opposite plate surface was referred to as comparativeexample 5. The brightness distributions of light exiting through thelight guide plates according to comparative examples 4 and 6 and theprism sheets were measured. Results are presented in FIG. 27. The lightguide plate according to comparative example 4 had a configuration inwhich structures are arranged on the plate surfaces of the light guideplate inversely from those on the light guide plate according tocomparative example 1 described in comparative experiment 2.Furthermore, each prism of the prism portion had a vertex angle of 140°.Each prism sheet had a configuration similar to the prism sheet of thefirst embodiment. In FIG. 27, the vertical axis represents relativebrightness levels of light exiting from the prism sheet (no unit) andthe horizontal axis represents angle relative to the direction towardthe front with respect to the second direction. The relative brightnesslevels represented by the vertical axis in FIG. 27 are expressed inbrightness levels relative to a reference (1.0) which is a brightnesslevel in the frontward direction (with an angle of 0°) on the lightguide plate according to each of the comparative examples 4 and 5. InFIG. 27, a solid line expresses the measurements of comparative example4 and a broken line expresses the measurements of comparative example 5.

The results of comparative experiment 6 will be described. FIG. 27describes that the frontward brightness levels related to light exitingfrom the prism sheet of comparative example 4 with respect to the seconddirection are higher than the frontward brightness levels of comparativeexample 5. Specifically, the light exiting through the light guide plateof comparative example 4 and the prism sheet include a larger amount oflight including light rays that travel in directions in a range ±10° ofthe frontward direction in comparison to the light exiting through thelight guide plate of comparative example 5 and the prism sheet. On theother hand, the light exiting through the light guide plate ofcomparative example 4 and the prism sheet include a larger amount oflight including light rays that travel in directions in a range from±20° to ±40° of the frontward direction in comparison to the lightexiting through the light guide plate of comparative example 5 and theprism sheet. Namely, a degree of collection of the light rays exitingthrough the light guide plate of comparative example 4 and the prismsheet with respect to the frontward direction is higher in comparison tocomparative example 5. Because comparative example 5 include the concavelenticular lens portion in the entire area of the opposite platesurface, the light rays to which the anisotropic light collectingeffects are added by the concave lenticular lens portion are less likelyto be collected by the prism sheet with respect to the second direction.Therefore, the frontward brightness levels may decrease. Becausecomparative example 4 includes the flat portion in the entire area ofthe opposite plate surface, specific optical effects are not added tothe light rays by the flat portion. Therefore, optical effects,specifically, the anisotropic light collecting effects are dominantlyadded to the light rays exiting from the light guide plate by the prismportion. The light rays are more likely to be collected with respect tothe second direction by the prism sheet. Therefore, the frontwardbrightness levels may become higher.

Comparative experiment 7 was conducted to determine how brightnesslevels varied as vertex angles of unit prisms of the prism portion werealtered. The light guide plate used in this experiment included a flatportion formed in an entire area of the opposite plate surface of thelight guide plate as in comparative example 4 in comparative experiment6 described above. In comparative experiment 7, the light guide plateaccording to comparative example 4 in comparative experiment 6 was used.The vertex angles of the unit prisms of the prism portion ware alteredin a range from 90° to 160°. Brightness levels of light exiting from thelight guide plate through the light exiting surface and through theprism sheet placed on a light exiting side of the light guide plate weremeasured. The brightness levels varied as the vertex angles werealtered. The results are presented in FIG. 28. In FIG. 28, thehorizontal axis represents vertex angle of the unit prisms (in unit of“°”) and the vertical axis represents relative brightness levels relatedto the light exiting from the prism sheet (in unit of “%”). The relativebrightness levels related to the exiting light represented by thevertical axis in FIG. 28 are expressed in brightness levels relative toa reference. A brightness level of light exiting through the light guideplate according to comparative example 5 in comparative experiment 6 andthe prism sheet was defined as the reference (100%).

The results of comparative experiment 7 will be described. FIG. 28describes that the relative brightness levels are higher when the vertexangles of the unit prisms are in a range from 102° to 112° or a rangefrom 132° to 156° in comparison to comparative example 5 in comparativeexperiment 6. When the vertex angles of the unit prisms were 110° or ina range from 135° to 155°, the relative brightness levels were 5% higherthan comparative example 5. When the vertex angles of the unit prismswere 150°, the brightness levels were the highest. The relativebrightness levels were 13% higher than comparative example 5. Becausethe flat portion was formed in the entire area of the opposite surfaceof the light guide plate in comparative experiment 7, specific opticaleffects were not added to the light rays by the flat portion. Therefore,optical effects, specifically, the anisotropic light collecting effectswere dominantly added to the light rays exiting from the light guideplate by the prism portion. The preferable vertex angle of the unitprisms of the prism portion is 110° or in the range from 135° to 155°, afurther preferable angle is in a range from 140° to 150°. This is alsoapplicable to the configuration in which the concave lenticular lensportion 114 having a width that vary according to the positions withrespect to the first direction and the flat portions 145 are formed onthe opposite plate surface 119 a of the light guide plate 119.

Comparative experiment 8 was conducted to determine differences inbrightness distribution between a configuration in which concavecylindrical lenses of concave lenticular lens portion had a constantwidth and a configuration in which the width was altered according topositions with respect to the first direction. In comparative experiment8, light guide plates having the following configurations were used. Thelight guide plate including concave cylindrical lenses on an oppositeplate surface having a width that was constant for an entire length ofthe light guide plate with respect to the first direction was referredto as comparative example 5. The light guide plate including the concavecylindrical lenses 144 a on the opposite plate surface 119 c having thewidth that gradually and continuously decreased as the distance from thelight entering surface 119 b with respect to the first directionincreased was referred to as embodiment 2. The brightness distributionsof the light guide plates were measured. Results of the measurement arepresented in FIGS. 29 to 31. On each of comparative example 5 andembodiment 2, the brightness distributions were measured at a positioncloser to the light entering surface with respect to the firstdirection, a position at the middle, and a position closer to theopposite end surface. Measurements at the position closer to the lightentering surface are presented in FIG. 29. Measurements at the positionin the middle are presented in FIG. 40. Measurements at the positioncloser to the opposite plate surface are presented in FIG. 31. The lightguide plate according to comparative example 5 has been described in theparagraphs about comparative experiment 6. The light guide plate 119according to embodiment 2 included the concave lenticular lens portion144 and the flat portions 145 on the opposite plate surface 119 c. Anoccupancy rate of the concave lenticular lens portion 144 with respectto the second direction varied according to the positions with respectto the first direction. The light guide plate 119 further included theexiting light reflecting portions 141 and the prism portion 143 on thelight exiting surface 119 a. In the area of the light guide plate 119according to embodiment 2 closer to the light entering surface 119 bwith respect to the first direction, the occupancy rate of the concavecylindrical lenses 144 a of the concave lenticular lens portion 144 withrespect to the second direction was higher and the occupancy rate of theflat portions 145 with respect to the second direction was lower. In thearea farther from the light entering surface 119 b with respect to thefirst direction, the occupancy rate of the concave cylindrical lenses144 a of the concave lenticular lens portion 144 with respect to thesecond direction was lower and the occupancy rate of the flat portions145 with respect to the second direction was higher. The detailedconfiguration of the light guide plate 119 has been described in theparagraphs prior to the paragraphs that describe comparative experiment6. The vertex angles of unit prisms 143 a of the prism portion 143 onthe light exiting surface 119 a of the light guide plate 119 accordingto embodiment 2 were 140°. In FIGS. 29 to 31, the vertical axisrepresents relative brightness levels of light exiting from the prismsheet (no unit) and the horizontal axis represents angle (in unit of“°”) relative to the frontward direction with respect to the seconddirection. The relative brightness levels represented by the verticalaxis in FIGS. 29 to 31 are expressed in brightness levels relative to areference. A brightness level with respect to the frontward direction(with the angle of 0°) on the light guide plate according to each ofcomparative example 5 and embodiment 2 was defined as the reference(1.0). In FIGS. 29 to 31, solid lines express the measurements ofcomparative example 5 and broken lines express the measurements ofembodiment 2.

The results of comparative experiment 8 will be described. According toFIGS. 29 to 31, frontward brightness levels of the light guide plate 119according to embodiment 2 are higher at any position with respect to thefirst direction in comparison to the light guide plate according tocomparative example 5. In comparison between FIG. 29 and FIG. 30, inembodiment 2, the frontward brightness level at the position in themiddle with respect to the first direction is higher than the frontwardbrightness at the position closer to the light entering surface withrespect to the first direction. In comparison between FIGS. 30 and 31,in embodiment 2, the frontward brightness level at the position closerto the opposite end surface with respect to the first direction ishigher than the frontward brightness level at the position in the middlewith respect to the first direction. Regarding the light guide plate 119according to embodiment 2, the frontward brightness level increased asthe distance from the light entering surface 119 b increased and thedistance to the opposite end surface 119 d decreased. Namely, thefrontward brightness level was inversely proportional to the variationin width of the concave cylindrical lenses 144 a. The width (or theoccupancy rate with respect to the second direction) of the concavecylindrical lenses 144 a was the largest at the end position on thelight entering surface 119 b side with respect to the first directionand the smallest at the end position on the opposite end surface 119 dside. As the width decreased, the frontward brightness level related tothe light exiting through the light guide plate 119 and the prism sheet142 was more likely to increase. With the concave cylindrical lenses 144a having the width that varied as described above and the width that waslarge on the light entering surface 119 b side with respect to the firstdirection, the uneven brightness with respect to the second directionwas properly reduced. At the middle or on the opposite end surface 119 dside with respect to the first direction where the uneven brightness wasgenerally less likely to occur, the width was small. Therefore, thefrontward brightness related to the light exiting from the prism sheetimproved. The measured brightness level of the light exiting through thelight guide plate 119 according to embodiment 2 and the prism sheet 142was about 8% higher than the configuration in which the light guideplate according to comparative example 5 was used.

As described above, this embodiment includes the reflecting memberopposed to the opposite plate surface 119 c of the light guide plate 119and including the reflecting surface for reflecting light. The exitinglight reflecting portions 141 and the prism portion 143 are on theopposite plate surface 119 c side of the light guide plate 119. Theconcave lenticular lens portion 144 is on the opposite plate surface 119c side of the light guide plate 119. According to the configuration, atleast some of light rays reflected by the unit reflectors 141 a of theexiting light reflecting portions 141 on the light exiting surface 119 aside of the light guide plate 119 travel toward the opposite platesurface 119 c. The anisotropic light collecting effects are added to thelight rays by the concave lenticular lens portion 144. The light rays towhich the anisotropic light collecting effects are added exit from thelight guide plate 119. The light rays that have exited from the lightguide plate 119 are reflected by the reflecting member and returned tothe opposite plate surface 119 c. The light rays enter the light guideplate 119 through the opposite plate surface 119 c and travel toward thelight exiting surface 119 a. The light rays to which the anisotropiclight collecting effects are added by the prism portion 143 exit theprism portion 143. Namely, the light rays reflected by the exiting lightreflecting portions 141 travel to the light exiting surface 119 a incomplicated paths. The light rays are subjected to refractive action atleast twice when the light rays exit from the opposite plate surfacetoward the reflecting member and when the light rays enter the oppositeplate surface 119 c from the reflecting member side. Among the lightrays reflected by the exiting light reflecting portions 141, the lightrays to which the anisotropic light collecting effects are not added bythe prism portion 143 are more likely to be diffused with respect to thesecond direction due to the refractive action described above.Therefore, the light rays are properly mixed and thus the unevenbrightness with respect to the second direction is less likely to occurin the light exiting from the light exiting surface 119 a.

The vertex angles θv2 of the unit prisms 143 a of the prism portion 143may be in the range from 135° to 155°. In comparison to theconfiguration in which the occupancy rate of the concave cylindricallenses with respect to the second direction is constant, thisconfiguration can sufficiently improve the brightness related to thelight exiting from the light exiting surface 119 a.

The vertex angles θv2 of the unit prisms 143 a of the prism portion 143may be 150°. In comparison to the configuration in which the occupancyrate of the concave cylindrical lenses with respect to the seconddirection is constant, this configuration can improve the brightnessrelated to the light exiting from the light exiting surface 119 afurther than any other configurations.

The vertex angles θv2 of the unit prisms 143 a of the prism portion 143may be 110°. In comparison to the configuration in which the occupancyrate of the concave cylindrical lenses with respect to the seconddirection is constant, this configuration can sufficiently improve thebrightness related to the light exiting from the light exiting surface119 a.

Third Embodiment

A third embodiment of the present invention will be described withreference to FIGS. 32 to 34. The third embodiment includes convexlenticular lens portion 46 instead of the concave lenticular lensportion 44 in the first embodiment. Configuration, functions, andeffects similar to those of the first embodiment will not be described.

As illustrated in FIG. 32, the convex lenticular lens portion(lenticular senses, light exiting surface-side lenticular senses) 46 isformed on a light exiting surface 219 a of a light guide plate 219according to this embodiment. The convex lenticular lens portion 46includes convex cylindrical lenses (cylindrical lenses, light exitingsurface-side cylindrical lenses) 46 a that extend along the firstdirection (or the X-axis direction). The convex cylindrical lenses 46 aare arranged along the second direction (or the Y-axis direction). Theconvex cylindrical lenses 46 a are convex lenses that protrude from thelight exiting surface 219 a toward the front (or the light exiting side)along the third direction (or the Z-axis direction). Each of the convexcylindrical lenses 46 a has a substantially semi-cylindrical shape withan axial direction thereof corresponding with the first direction. Aback surface of each convex cylindrical lens 46 a on the rear side isarched and referred to as an arched surface 46 a 1. Each convexcylindrical lens 46 a has a substantially semicircular cross sectionalong an arrangement direction (or the second direction), which isperpendicular to an extending direction (or the first direction). Eachconvex cylindrical lens 46 a has a width (or a dimension in the seconddirection) which is constant in the first direction for an entire lengththereof. A “tangent angle” of each convex cylindrical lens 46 a is anangle of a tangent line Ta at a base end 46 a 2 of the arched surface 46a 1 relative to the second direction. The tangent angle θt may be about70°.

The cylindrical lenses 46 a having such a configuration exert opticaleffects substantially the same as the optical effects exerted by theconcave cylindrical lenses 44 a of the first embodiment describedearlier (see FIGS. 10 to 12). If light rays that have reached the lightexiting surface 219 a enter the arched surfaces 46 a 1 of the convexcylindrical lenses 46 a with angles of incidence larger than thecritical angle, the light rays are totally reflected by the archedsurfaces 46 a 1. As a result, the light rays travel through the lightguide plate 219 while diffusing in a wide area with respect to thesecond direction. According to the configuration, uneven brightness withrespect to the second direction is less likely to occur. Furthermore, ifthe light rays that have reached the light exiting surface 219 a enterthe arched surface 46 a 1 of the convex cylindrical lenses 46 a with theangles of incidence equal to or smaller than the critical angle, thelight rays are refracted at the arched surfaces 46 a 1 and directed tothe prism sheet.

As illustrated in FIGS. 32 to 34, the convex cylindrical lens 46 a ofthe convex lenticular lens portion 46 has widths (or dimensions in thesecond direction) which vary according to positions with respect to thefirst direction. The widths of the convex cylindrical lenses 46 a, thatis, an occupancy rate of the convex cylindrical lenses 46 a with respectto the second direction in the light exiting surface 219 a gradually andcontinuously decreases as a distance from the light entering surfacewith respect to the first direction increases and a distance to theopposite end surface decreases. The widths, that is, the occupancy rategradually and continuously increases as the distance from the oppositeend surface with respect to the first direction increases and thedistance to the light entering surface decreases. The occupancy rate ofthe convex cylindrical lenses 46 a is at a maximum in an end portion (orat an end position) of the light guide plate 219 on the light enteringsurface side with respect to the first direction and in a range from 70%to 90%. In an end portion on the opposite end surface side, theoccupancy rate is at a minimum and in a range from 10% to 30%. In themiddle portion with respect to the first direction, the occupancy rateis about 50%. Furthermore, the convex cylindrical lenses 46 a haveheights (or dimensions in the third direction) which vary according topositions with respect to the first direction. The heights of the convexcylindrical lenses 46 a, that is, dimensions from the light exitingsurface 219 a gradually and continuously decrease as a distance from thelight entering surface with respect to the first direction increases anda distance to the opposite end surface decreases. Furthermore, theheights gradually and continuously increase as a distance from theopposite end surface with respect to the first direction increases and adistance to the light entering surface decreases. Namely, the heights ofthe convex cylindrical lenses 46 a vary according to the positions withrespect to the first direction, similarly to the widths. Therefore, asurface area of the convex cylindrical lenses 46 a (or an area of thearched surfaces 46 a 1) varies according to positions of the firstdirection, similarly to the widths and the heights.

In an area of the light exiting surface 219 a of the light guide plate219 in which the convex lenticular lens portion 46 (or the convexcylindrical lenses 46 a) is not formed, flat portions 245 are formed.The flat portions 245 are flat along the first direction (or the X-axisdirection) and the second direction (or the Y-axis direction). The flatportions 245 are arranged adjacent to the convex cylindrical lenses 46 awith respect to the second direction. Namely, the convex cylindricallenses 46 a and the flat portions 245 are alternately arranged on thelight exiting surface 219 a of the light guide plate 219 with respect tothe second direction. The flat portions 245 have widths (or dimensionsin the second direction) which vary according to positions with respectto the first direction. The widths of the flat portions 245, that is, anoccupancy rate of the flat portions 245 with respect to the seconddirection in the light exiting surface 219 a gradually and continuouslydecreases as a distance to the light entering surface with respect tothe first direction decreases and a distance from the opposite endsurface increases. Furthermore, the widths or the occupancy rategradually and continuously increases as a distance to the opposite endsurface with respect to the first direction decreases and a distancefrom the light entering surface increases. The occupancy rate of theflat portions 245 is at a minimum in an end portion (or at an endposition) of the light guide plate 219 on the light entering surfaceside with respect to the first direction and in a range from 10% to 30%.In an end portion on the opposite end surface side, the occupancy rateis at a maximum and in a range from 70% to 90%. In the middle portionwith respect to the first direction, the occupancy rate is about 50%.

Regarding the convex lenticular lens portion 46 and the flat portions245, in the portion closer to the light entering surface with respect tothe first direction, the occupancy rate of the convex cylindrical lenses46 a with respect to the second direction in the light exiting surface219 a of the light guide plate 219 c is higher and the occupancy rate ofthe flat portions 245 with respect to the second direction in the lightexiting surface 219 a of the light guide plate 219 c is lower. In theportion farther from the light entering surface with respect to thefirst direction, the occupancy rate of the convex cylindrical lenses 46a is lower and the occupancy rate of the flat portions 245 is higher. Inthe portion closer to the light entering surface with respect to thefirst direction in which uneven brightness due to the LEDs that are notillustrated may occur, uneven brightness with respect to the seconddirection is less likely to occur in light exiting from the prism sheetthat is not illustrated because of the convex cylindrical lenses 46 a.In the portion farther from the light entering surface with respect tothe first direction in which the uneven brightness due to the LEDs isless likely to occur, the brightness of the light exiting from the prismsheet is further improved by the flat portions 245 having the higheroccupancy rate. According to the configuration, the uneven brightness inthe light exiting from the prism sheet is reduced and the brightness ofthe light is improved.

According to this embodiment, the convex lenticular lens portion 46includes the convex cylindrical lenses 46 a that are formed to protrude.In comparison to a configuration in which the cylindrical lenses areformed to concave, the light rays traveling through the light guideplate 219 are more likely to enter interfaces of the convex cylindricallenses 46 a having curved shapes with angles of incidence smaller thanthe critical angle. Therefore, the light rays are more likely to exitfrom the interfaces.

Fourth Embodiment

A fourth embodiment of the present invention will be described withreference to FIG. 35. The fourth embodiment includes a convex lenticularlens portion 346 having a configuration different from the configurationof the convex lenticular lens portion in the third embodiment.Configuration, functions, and effects similar to those of the thirdembodiment will not be described.

As illustrated in FIG. 35, the lenticular lens portion 346 according tothis embodiment includes convex cylindrical lenses 346 a. The convexcylindrical lenses 346 a include first convex cylindrical lenses (firstcylindrical lenses) 346 aA and second convex cylindrical lenses (secondcylindrical lenses) 346 aB. The first convex cylindrical lenses 346 aAhave smaller heights and the second convex cylindrical lenses 346 aBhave larger heights. The first convex cylindrical lenses 346 aA and thesecond convex cylindrical lenses 346 aB have widths and heights thatvary in the same manner as those of the convex cylindrical lenses 46 ain the third embodiment described above. Furthermore, the first convexcylindrical lenses 346 aA and the second convex cylindrical lenses 346aB have tangent angles the same as tangent angles of the convexcylindrical lenses 46 a in the third embodiment. Namely, each of thefirst convex cylindrical lenses 346 aA has a cross section similar tothe cross section of each of the second convex cylindrical lenses 346aB.

A width of a bottom surface and the heights of each second convexcylindrical lens 346 aB are larger than those of each first convexcylindrical lens 346 aA. Specifically, the width of a bottom surface andthe height of each second convex cylindrical lens 346 aB are aboutdouble of the width and the height of each first convex cylindrical lens346 aA, respectively. Vertices 346 aB1 of the second convex cylindricallenses 346 aB are arranged at positions higher (or closer to a prismsheet 342) than positions at which vertices 346 aA1 of the first convexcylindrical lenses 346 aA to contact with a back plate surface of theprism sheet 342 on the rear side (or a light guide plate 319 side). Thevertices 346 aA1 of the first convex cylindrical lenses 346 aA arearranged at the positions lower (or farther from the prism sheet 342)than the positions at which the vertices 346 aB1 of the second convexcylindrical lenses 346 aB are arranged. Clearances C2 are providedbetween the back plate surface of the prism sheet 342 and the vertices346 aA1 of the first convex cylindrical lenses 346 aA. Namely, the firstconvex cylindrical lenses 346 aA are not in contact with the back platesurface of the prism sheet 342. According to the configuration, acontact area between the light guide plate 319 and the prism sheet 342is smaller in comparison to the third embodiment. Furthermore, theclearances C2, which are air layers, are provided between the lightguide plate 319 and the prism sheet 342 and thus the light guide plate319 and the prism sheet 342 are less likely to be in close contact witheach other. Flat portions 345 are sandwiched between the first convexcylindrical lenses 346 aA and the second convex cylindrical lenses 346aB that are adjacent to one another with respect to the seconddirection.

As described above, in this embodiment, exiting light reflectingportions 341 and prism portions 343 are arranged on an opposite platesurface 319 c side of the light guide plate 319 and the convexlenticular lens portion 346 is arranged on a light exiting surface 319 aside of the light guide plate 319. The convex cylindrical lenses 346 aof the convex lenticular lens portion 346 include the first convexcylindrical lenses (the first cylindrical lenses) 346 aA having thesmaller heights and the second convex cylindrical lenses (the secondcylindrical lenses) 346AB having the larger heights. Furthermore, theclearances C2 are provided between the first convex cylindrical lenses346 aA and the prism sheet 342. With the clearances C2 between the firstconvex cylindrical lenses 346 aA of the convex cylindrical lenses 346 aand the prism sheet 342, the prism sheet 342 is less likely to be inclose contact with the convex lenticular lens portion 346. Therefore,uneven brightness is less likely to occur in light exiting from thebacklight unit 312.

Fifth Embodiment

A fifth embodiment of the present invention will be described withreference to FIGS. 36 to 38. The fifth embodiment includes a convexlenticular lens portion 446 similar to the convex lenticular lensportion in the third embodiment instead of the concave lenticular lensportion 144 in the second embodiment. Configuration, functions, andeffects similar to those of the second and the third embodiments willnot be described.

As illustrated in FIGS. 36 to 38, a light guide plate 419 according tothis embodiment includes exiting light reflecting portions 441 and prismportions 443 on an opposite plate surface 419 c side and the convexlenticular lens portion 446 and flat portions 445 on a light exitingsurface 419 a side. Arrangements of structures on the plate surfaces ofthe light guide plate 419 are reversed from the arrangements of thestructures on the plate surfaces 219 a and 219 c of the light guideplate 219 in the third embodiment described earlier. Configurations ofthe exiting light reflecting portions 441, the prism portions 443, theconvex lenticular lens portion 446, and the flat portions 445 aresimilar to those of the third embodiment except for the arrangements onthe plate surfaces 419 a and 419 c of the light guide plate 419. Withthe convex lenticular lens portion 446, the opposite plate surface 419 cof the light guide plate 419 has an irregular shape. Therefore, certainclearances are provided between convex cylindrical lenses 446 a arrangedalong the second direction and a reflection sheet that is notillustrated.

Sixth Embodiment

A sixth embodiment of the present invention will be described withreference to FIG. 39. The sixth embodiment includes a concave lenticularlens portion 544 and flat portions 545 having occupancy rates withrespect to the second direction different from the occupancy rates inthe first embodiment. Configuration, functions, and effects similar tothose of the first embodiment will not be described.

As illustrated in FIG. 39, the concave lenticular lens portion 544according to this embodiment includes concave cylindrical lenses 544 aformed such that an occupancy rate thereof with respect to the seconddirection in an end portion of a light exiting surface 519 a on anopposite end surface 519 d side is substantially 0%. Flat portions 545are formed such that an occupancy rate thereof with respect to thesecond direction in the end portion of the light exiting surface 519 aon the opposite end surface 519 d side is substantially 100%. Thisconfiguration is especially practical in a case that a sufficient levelof brightness cannot be achieved on the opposite end surface 519 d sideof the light guide plate 519.

Seventh Embodiment

A seventh embodiment of the present invention will be described withreference to FIG. 40. The seventh embodiment includes a convexlenticular lens portion 644 and flat portions 645 having occupancy rateswith respect to the second direction different from those of the sixthembodiment. Configuration, functions, and effects similar to those ofthe first and the sixth embodiments will not be described.

As illustrated in FIG. 40, the concave lenticular lens portion 644according to this embodiment includes concave cylindrical lenses 644 aformed such that an occupancy rate thereof with respect to the seconddirection in an end portion of a light exiting surface 619 a on anopposite end surface 619 d side is substantially 0% and in an endportion of the light exiting surface 619 a on a light entering surface619 b side is substantially 100%. The flat portions 645 are formed suchthat an occupancy rate thereof with respect to the second direction inthe end portion of the light exiting surface 619 a on the opposite endsurface 619 d side is substantially 100% and in the end portion of thelight exiting surface 619 a on the light entering surface 619 b side issubstantially 0%. This configuration is especially practical in a casethat a sufficient level of brightness cannot be achieved on the oppositeend surface 619 d side of the light guide plate 619 and unevenbrightness is more likely to occur on the light entering surface 619 bside.

Eighth Embodiment

An eighth embodiment of the present invention will be described withreference to FIG. 41. The eighth embodiment includes a convex lenticularlens portion 744 and flat portions 745 having occupancy rates withrespect to the second direction different from the occupancy rates inthe seventh embodiment. Configuration, functions, and effects similar tothose of the first and the seventh embodiments will not be described.

As illustrated in FIG. 41, the convex lenticular lens portion 744according to this embodiment includes concave cylindrical lenses 744 aformed such that an occupancy rate thereof with respect to the seconddirection in a light exiting surface 719 a gradually and continuouslydecreases as a distance from a light entering surface 719 b with respectto the first direction increases and the occupancy rate reaches 0% at apoint before reaching an end on an opposite end surface 719 d side. Adimension of an area in which the concave lenticular lens portion 744 isformed with respect to the first direction is smaller than the length ofa light guide plate 719. The area is from an end on the light enteringsurface 719 b side to the point before reaching the opposite end surface719 d. The flat portions 745 are formed such that an occupancy ratethereof with respect to the second direction in the light exitingsurface 719 a gradually and continuously increases as a distance fromthe light entering surface 719 b with respect to the first directionincreases and the occupancy rate reaches 100% at a point before reachingthe end on the opposite end surface 719 d side. This configuration isespecially practical in a case that the sufficient level of brightnessis further less likely to be achieved on the opposite end surface 719 dside of the light guide plate 719.

Ninth Embodiment

A ninth embodiment of the present invention will be described withreference to FIG. 42. The ninth embodiment includes a convex lenticularlens portion 844 and flat portions 845 having occupancy rates withrespect to the second direction different from those of the firstembodiment. Configuration, functions, and effects similar to those ofthe first embodiment will not be described.

As illustrated in FIG. 42, the concave lenticular lens portion 844 (orconcave cylindrical lenses 844 a) and the flat portions 845 according tothis embodiment include side edges SE that define widths of the concavecylindrical lenses 844 a and the flat portions 845. The side edges SEare curved in a plan view. The concave lenticular lens portion 844 andthe flat portions 845 are formed such that the side edges SE run onconcave cylindrical lens 844 a side relative to imaginal lines L betweenends of the side edges SE with respect to the first direction and otherends of the side edges SE, respectively (indicated by two-dot chainlines in FIG. 42). According to the configuration, improvement ofbrightness and reduction of uneven brightness can be achieved at thesame time, similarly to the first embodiment described earlier.

Tenth Embodiment

A tenth embodiment of the present invention will be described withreference to FIG. 43. The tenth embodiment includes a concave lenticularlens portion 944 and flat portions 945 having occupancy rates withrespect to the second direction different from those of the firstembodiment. Configuration, functions, and effects similar to those ofthe first embodiment will not be described.

As illustrated in FIG. 43, the concave lenticular lens portion 944 (orconcave cylindrical lenses 944 a) and the flat portions 945 according tothis embodiment include side edges SE that define widths of the concavecylindrical lenses 944 a and the flat portions 945. The side edges SEare curved in a plan view. The concave lenticular lens portion 944 andthe flat portions 945 are formed such that the side edges SE run on flatportion 945 side relative to imaginary lines L between ends of the sideedges SE with respect to the first direction and other ends of the sideedges SE, respectively (indicated by two-dot chain lines in FIG. 43).According to the configuration, improvement of brightness and reductionof uneven brightness can be achieved at the same time, similarly to thefirst embodiment described earlier.

Eleventh Embodiment

An eleventh embodiment of the present invention will be described withreference to FIG. 44. The eleventh embodiment includes a concavelenticular lens portion 1044 and flat portions 1045 having occupancyrates with respect to the second direction different from the occupancyrates in the first embodiment. Configuration, functions, and effectssimilar to those of the first embodiment will not be described.

As illustrated in FIG. 44, the concave lenticular lens portion 1044 (orconcave cylindrical lenses 1044 a) and the flat portions 1045 accordingto this embodiment include side edges SE that define widths of theconcave cylindrical lenses 1044 a and the flat portions 1045. Each sideedge SE is angled twice in a plan view. Occupancy rates of the concavelenticular lens portion 1044 and the flat portions 1045 with respect tothe second direction in a light exiting surface 1019 a vary according topositions with respect to the first direction. Variation rates of theoccupancy rates are altered at specified points. The side edges SE ofthe concave lenticular lens portion 1044 and the flat portions 1045include first angle side edges SE1 and second angle side edges SE2.Angles of the first angle side edges SE1 are larger and angles of thesecond angle side edges SE2 are smaller. Boundaries between the firstangle side edges SE1 and the second angle side edges SE2 substantiallycorrespond with the middle of a light guide plate 1019 with respect tothe first direction. According to the configuration, improvement ofbrightness and reduction of uneven brightness can be achieved at thesame time, similarly to the first embodiment described earlier.

Twelfth Embodiment

A twelfth embodiment of the present invention will be described withreference to FIG. 45. The twelfth embodiment includes a concavelenticular lens portion 1144 and flat portions 1145 having occupancyrates with respect to the second direction different from those of thefirst embodiment. Configuration, functions, and effects similar to thoseof the first embodiment will not be described.

As illustrated in FIG. 45, the concave lenticular lens portion 1144 andthe flat portions 1145 according to this embodiment include side edgesSE that define width thereof. Each side edge SE is angled multiple timesin a plan view. The concave lenticular lens portion 1144 is formed suchthat an occupancy rate of concave cylindrical lenses 1144 a with respectto the second direction in a light exiting surface 1119 a of a lightguide plate 1119 decreases stepwise as a distance from a light enteringsurface 1119 b with respect to the first direction increases and adistance to an opposite end surface 1119 d decreases. An occupancy rateof the flat portions 1145 increases stepwise as the distance from thelight entering surface 1119 b with respect to the first directionincreases and the distance to the opposite end surface 1119 d decreases.The side edges SE of the concave lenticular lens portion 1144 and theflat portions 1145 include portions parallel to the first direction andportions parallel to the second direction alternately connected to oneanother. In this embodiment, the widths of the concave lenticular lensportion 1144 and the flat portions 1145 are increased or decreased fivetimes.

Thirteenth Embodiment

A thirteenth embodiment of the present invention will be described withreference to FIG. 46. The thirteenth embodiment includes two LED boards1218 including LEDs 1217 disposed on either side of a light guide plate1219. Configuration, functions, and effects similar to those of thefirst embodiment will not be described. According to the configuration,improvement of brightness and reduction of uneven brightness can beachieved at the same time, similarly to the first embodiment describedearlier.

As illustrated in FIG. 46, two LED boards 1218 including the LEDs 1217according to this embodiment are disposed to sandwich the light guideplate 1219 from sides with respect to the first direction (or the X-axisdirection). End surfaces on short sides among end surfaces of the lightguide plate 1219 are configured as light entering surfaces 1219 bthrough which light rays from the LEDs 1217 enter. End surfaces 1219 eon long sides are configured as non-light entering surfaces throughwhich light rays from the LEDs 1217 are not directly enter. In FIG. 46,the LEDs 1217 and the LED boards 1218 are indicated by two-dot chainlines.

To arrange the LED boards 1218 as described above, a concave lenticularlens portion 1244 and flat portions 1245 on a light exiting surface 1219a of the light guide plate 1219 are configured as follows. The concavelenticular lens portion 1244 is formed such that an occupancy rate ofconcave cylindrical lenses 1244 a with respect to the second directionin the light exiting surface 1219 a is higher on the light enteringsurface 1219 b side with respect to the first direction and lower in themiddle with respect to the first direction. The flat portions 1245 areformed such that an occupancy rate thereof is lower on the lightentering surface 1219 b side with respect to the first direction andhigher in the middle with respect to the first direction.

Specifically, the concave lenticular lens portion 1244 is formed suchthat the occupancy rate (or widths) of the concave cylindrical lenses1244 a with respect to the second direction in the light exiting surface1219 a gradually and continuously decreases as a distances from eitherone of the light entering surfaces 1219 b with respect to the firstdirection increases and a distance to the middle position with respectto the first direction (or to a position the farthest from either one ofthe light entering surfaces 1219 b) decreases. The occupancy rategradually and continuously increases as a distance from the middle withrespect to the first direction increases and a distance to either one ofthe light entering surfaces 1219 b decreases. The occupancy rate of theconcave cylindrical lenses 1244 a is at a maximum in end portions(closer to edges) of the light guide plate 1219 on the light enteringsurface 1219 b sides with respect to the first direction. The occupancyrate may be in a range from 70% to 90%. The occupancy rate is at aminimum in the middle with respect to the first direction. The occupancyrate may be in a range from 10% to 30%. The occupancy rate of the flatportions 1245 gradually and continuously increases as the distance fromeither one of the light entering surfaces 1219 b with respect to thefirst direction increases and the distance to the middle with respect tothe first direction decreases. The occupancy rate gradually andcontinuously decreases as the distance from the middle with respect tothe first direction increases and the distance to either one of thelight entering surfaces 1219 b decreases. The occupancy rate of the flatportions 1245 is at a minimum in the end portions of the light guideplate 1219 on the light entering surface 1219 b sides with respect tothe first direction. The occupancy rate may be in a range from 10% to30%. The occupancy rate is at a maximum in the middle portion withrespect to the first direction. The occupancy rate is in a range from70% to 90%. Variation rates in the occupancy rates of the concavelenticular lens portion 1244 and the flat portions 1245 are equal toeach other. According to the configuration, improvement of brightnessand reduction of uneven brightness can be achieved at the same time,similarly to the first embodiment described earlier.

Other Embodiment

The present invention is not limited to the above embodiments describedwith reference to the drawings. The following embodiments may beincluded in the technical scope of the present invention.

(1) The occupancy rates of the concave cylindrical lenses and the convexcylindrical lenses with respect to the second direction in the oppositeplate surfaces or the light exiting surfaces of the light guide platesmay be altered from those in the above embodiments as appropriate. Theoccupancy rates in the end portions on the light entering surface sideswith respect to the first direction may be in a range from 90% to 100%or a range from 50% to 70% and the occupancy rates in the end portionson the opposite end surface sides may be in a range from 0% to 10% or arange from 30% to 50%. The occupancy rates of the concave cylindricallenses or the concave cylindrical lenses with respect to the seconddirection in the middle portions of the opposite plate surfaces of thelight guide plates with respect to the first direction and the occupancyrates of the flat portions may be different from one another.

(2) The occupancy rates of the flat portions with respect to the seconddirection in the opposite plate surfaces or the light exiting surfacesof the light guide plates may be altered from the occupancy rates of theabove embodiments. The occupancy rates in the end portions on the lightentering surface sides with respect to the first direction may be in arange from 0% to 10% or a range from 30% to 50% and the occupancy ratesin the end portions on the opposite end surface sides with respect tothe first direction may be in a range from 90% to 100% or a range from50% to 70%.

(3) Other than the above embodiments, the occupancy rates of the concavecylindrical lenses or the convex cylindrical lenses and the occupancyrates of the flat portions with respect to the second direction in themiddle portions of the light exiting surfaces or the opposite platesurfaces of the light guide plates with respect to the first directionmay be different from one another. In such configurations, the portionsin which the occupancy rates are equal to one another may be alteredfrom the middle portions with respect to the first direction to portionscloser to either the light entering surfaces or the opposite endsurfaces.

(4) In each of the above embodiments, the flat portions and the concavecylindrical lenses or the convex cylindrical lenses are alternately andrepeatedly arranged in the second direction. However, the concavecylindrical lenses or the convex cylindrical lenses may be consecutivelyarranged in the second direction and multiple concave cylindrical lensesor multiple convex cylindrical lenses adjacent to one another may besandwiched between the flat portions.

(5) In each of the above embodiments, the flat portions are formed onthe opposite plate surface or the light exiting surface of the lightguide plate. However, the flat portions may be formed on the oppositeplate surface and the light exiting surface of the light guide plate ineach of the above embodiments. In such a configuration, a prism portionmay be formed and the flat portions may be arranged between unit prismsarranged along the second direction.

(6) In each of the above embodiments, each unit prism of the prismportion has the isosceles triangular cross section. However, each unitprism may have a scalene triangular cross section with all sides ofdifferent lengths or an isosceles right triangular cross section.

(7) The vertices, the heights, and the widths of the unit prisms of theprism portion and the intervals of the unit prisms with respect to thesecond direction may be altered from those of the above embodiments asappropriate. The vertices, the heights, and the widths of the lightexiting-side unit prisms of the prism sheet and the intervals of thelight exiting-side unit prisms with respect to the second direction maybe altered from the vertices, the heights, and the width in the aboveembodiments as appropriate.

(8) The tangent lines, the heights, and the widths of the convexcylindrical lenses of the convex lenticular lens portion or the tangentlines, the heights, and the widths of the concave cylindrical lenses ofthe concave lenticular lens portion and the intervals of the convexcylindrical lenses or the concave cylindrical lenses may be altered fromthe tangent lines, the heights, the widths, and the intervals in theabove embodiments as appropriate.

(9) In each of the above embodiments, the exiting light reflectingportions and the prism portion are integrally formed with the oppositeplate surface or the light exiting surface of the light guide plate.However, the exiting light reflecting portions and the prism portion maybe prepared as separate parts and disposed over the opposite platesurface or the light exiting surface. In such a configuration, it ispreferable that the exiting light reflecting portions and the prismportion prepared as the separate parts are made of materials having thesame refractive index as the refractive index of the material of thelight guide plate. It is more preferable that the exiting lightreflecting portions and the prism portion are made of the same materialas the material of the light guide plate.

(10) In each of the above embodiments, the convex lenticular lensportion or the concave lenticular lens portion and the flat portions areintegrally formed with the light exiting surface or the opposite platesurface of the light guide plate. However, the convex lenticular lensportion or the concave lenticular lens portion and the flat portions maybe prepared as separate parts and disposed over the light exitingsurface or the opposite plate surface of the light guide plate. In sucha configuration, it is preferable that the convex lenticular lensportion or the concave lenticular lens portion and the flat portionsprepared as the separate parts may be made of materials having the samerefractive index as the refractive index of the material of the lightguide plate. It is more preferable that the convex lenticular lensportion or the concave lenticular lens portion and the flat portionsprepared as the separate parts may be made of the same material as thematerial of the light guide plate.

(11) The configurations of the sixth to the thirteenth embodiments maybe combined with any configurations of the second to the fifthembodiments.

(12) Each of the above embodiments includes the specular reflectionsheet. However, a diffuse reflection sheet may be used.

(13) Each of the above embodiments includes the optical sheet thatincludes a single prism sheet. However, other types of optical sheets(e.g., a diffuser and a reflection type polarizing sheet) may be addedto the optical sheet. Furthermore, the optical sheet may includemultiple prism sheets.

(14) In each of the above embodiments, a single LED board is disposedalong the light entering surface of the light guide plate. However, aconfiguration including two or more LED boards disposed along the lightentering surface of the light guide plate may be included in the scopesof the present invention.

(15) Each first convex cylindrical lens and each second convexcylindrical lens in the fourth embodiment described earlier have thesimilar cross sections. However, a configuration including first convexcylindrical lenses and second convex cylindrical lenses havingnon-similar cross sections may be included in the scopes of the presentinvention. For example, the first convex cylindrical lenses may havetangent angles or curvatures different from tangent angles or curvaturesof the second convex cylindrical lenses.

(16) The convex lenticular lens portion of the fourth embodimentdescribed earlier includes two types of the convex cylindrical lenses.However, the convex lenticular lens portion may include three or moretypes of convex cylindrical lenses having different heights.

(17) A modification of the fourth embodiment described earlier mayinclude second convex cylindrical lenses with round vertices. Accordingto the configuration, the back plate surface of the prism sheet is lesslikely to be scratched.

(18) In the eleventh embodiment described above, the concave cylindricallenses and the flat portions include the side edges that define thewidths of the concave cylindrical lenses and the flat portions. The sideedges are angled twice in a plan view. However, the side edges may beangled three or more times in a plan view.

(19) In the twelfth embodiment described earlier, the widths of theconcave cylindrical lenses and the flat portions are increased ordecreased five times according to the positions with respect to thefirst direction. However, the widths may be increased or decreased fourtimes or less. Furthermore, the widths may be increased or decreased sixtimes or more.

(20) In each of the above embodiments (except for the thirteenthembodiment), one of the short peripheral surfaces of the light guideplate is configured as a light entering surface and the LED board isdisposed opposite the light entering surface. However, one of the longperipheral surfaces of the light guide plate may be configured as alight entering surface and the LED board may be disposed opposite thelight entering surface. The direction in which the light exiting-sideunit prisms, the unit prisms, and the convex cylindrical lenses (or theconcave cylindrical lenses) extend may be aligned with the short-sidedirection of the light guide plate. Furthermore, the width directions(or the arrangement directions) of the light exiting-side unit prisms,the unit prisms, and the convex cylindrical lenses (or the concavecylindrical lenses) may be aligned with the long-side direction of thelight guide plate.

(21) A modification of the thirteenth embodiment may have aconfiguration in which both long peripheral surfaces are configured aslight entering surfaces and LED boards are disposed opposite the longperipheral surfaces, respectively, may be included in the scope of thepresent invention.

(22) In each of the above embodiments, the light guide plate has therectangular shape. However, the light guide plate may have a squareshape. Furthermore, the shape of the light guide plate does not need tobe complete rectangular. A part of the periphery of the light guideplate may be cut.

(23) In each of the above embodiments, the top surface light emittingtype LEDs are used. However, the present invention may be applied to aconfiguration that includes side surface light emitting LEDs. The sidesurface light emitting LED includes a side surface adjacent to themounting surface that is mounted to the LED board and configured as alight emitting surface.

(24) In each of the above embodiments, the touchscreen pattern using theprojected capacitive touchscreen technology is used. Other than that,the present invention may be applied to configurations that include atouchscreen pattern using the surface capacitive touchscreen technology,a touchscreen pattern using the resistive touchscreen technology, and atouchscreen pattern using the electromagnetic induction touchscreentechnology, respectively.

(25) Instead of the touchscreen in each of the above embodiments, aparallax barrier panel (a switching liquid crystal panel) includingparallax barrier patterns may be used. The parallax barrier patterns arefor separating images displayed on the liquid crystal panel with aparallax so that a user sees stereoscopic images (3D images,three-dimensional images). The parallax barrier panel may be used incombination with the touchscreen panel.

(26) Touchscreen patterns may be formed on the parallax barrier panel inembodiment (25) to add touchscreen functions to the parallax barrierpanel.

(27) In each of the above embodiments, the liquid crystal panel of theliquid crystal display device has the screen size of about 20 inches.The screen size of the liquid crystal panel may be altered asappropriate.

(28) In each of the above embodiments, the color portions of the colorfilters of the liquid crystal panel are in three colors of R, G and B.However, the color portions may be in four or more colors.

(29) In each of the above embodiments, the LEDs are used as lightsources. However, organic ELs or other types of light sources may beused.

(30) In each of the above embodiments, the frame is made of metal.However, the frame may be made of synthetic resin.

(31) In each of the above embodiments, the chemically toughened glass isused for the cover panel. However, a toughened glass prepared with anair-cooling toughening process (a physically toughening process)performed thereon may be used.

(32) In each of the above embodiments, the chemically toughened glass isused for the cover panel. However, a regular glass (non-toughened glass)other than the toughened glass or a synthetic resin member may be used.

(33) In each of the above embodiments, the cover panel is used for theliquid crystal display device. However, the cover panel may not be used.Furthermore, the touchscreen panel may not be used. Still furthermore,some of the components of the liquid crystal display device may beomitted as appropriate.

(34) Each of the above embodiments includes the TFTs as switchingcomponents of the liquid crystal display device. However, switchingcomponents other than the TFTs (such as thin film diodes (TFDs)) may beincluded in the scope of the present invention. Furthermore, a liquidcrystal display device configured to display black and white imagesother than the liquid crystal display device configured to display colorimages.

EXPLANATION OF SYMBOLS

-   -   10: Liquid crystal display device (a display device)    -   11: Liquid crystal panel (a display panel)    -   12, 312: Backlight unit (a lighting device)    -   17, 1217: LED (a light source)    -   19, 119, 219, 319, 419, 519, 619, 719, 1019, 1119, 1219: Light        guide plate    -   19 a, 119 a, 219 a, 319 a, 419 a, 519 a, 619 a, 719 a, 1019 a,        1119 a, 1219 a: Light exiting surface    -   19 b, 119 b, 619 b, 719 b, 1119 b, 1219 b: Light entering        surface    -   19 c, 119 c, 319 c, 419 c: Opposite plate surface    -   40, 140, 340: Reflection sheet (a reflecting member)    -   40 a, 140 a, 340 a: Reflection surface    -   41, 141, 341, 441: Exiting light reflecting portion    -   41 a: Unit reflector    -   42, 142, 342: Prism sheet (light exiting-side anisotropic light        collecting portion)    -   42 a: Light exiting-side unit prism (light exiting-side unit        light collector)    -   43, 143, 343, 443: Prism portion    -   43 a: Unit prism    -   44, 144, 544, 644, 744, 844, 944, 1044, 1144, 1244: Concave        lenticular lens portion (lenticular lens portion)    -   44 a, 144 a, 544 a, 644 a 744 a, 844 a, 944 a, 1044 a, 1144 a,        1244 a: Concave cylindrical lens (cylindrical lens)    -   45, 145, 245, 345, 445, 545, 645, 745, 845, 945, 1045, 1145,        1245: Flat portion    -   46, 346, 446: Convex lenticular lens portion (lenticular lens        portion)    -   46 a, 346 a, 446 a: Convex cylindrical lens (cylindrical lens)    -   346 aA: First convex cylindrical lens (first cylindrical lens)    -   346 aB: Second convex cylindrical lens (second cylindrical lens)    -   θv2: Vertex angle    -   C1: Clearance    -   C2: Clearance

The invention claimed is:
 1. A lighting device comprising: a lightsource; a light guide plate having a rectangular plate shape andincluding peripheral end surfaces opposite from each other and platesurfaces, at least one of the peripheral end surfaces being configuredas a light entering surface through which light emitted by the lightsource enters, one of the plate surfaces being configured as a lightexiting surface through which the light exits, the other one of theplate surfaces being defined as an opposite surface; a lightexiting-side anisotropic light collecting portion formed on a lightexiting side and including light exiting-side unit light collectorsextending along a first direction parallel to peripheral end surfaces ofthe light guide plate not including the light entering surface, the unitlight collectors being arranged parallel to one another along a seconddirection parallel to the peripheral end surfaces including the lightentering surface; an exiting light reflecting portion formed on one of alight exiting surface side and an opposite plate surface side of thelight guide plate for reflecting light traveling through the light guideplate such that the light exits from the light exiting surface, theexiting light reflecting portion including unit reflectors extendingalong the second direction and being arranged at intervals along thefirst direction; a prism portion formed on one of the light exitingsurface side and the opposite plate surface side of the light guideplate, the prism portion including unit prisms extending along the firstdirection and being arranged along the second direction; a lenticularlens portion formed on the other one of the light exiting surface andthe opposite plate surface of the light guide plate, the lenticular lensportion including cylindrical lenses extending along the first directionand being arranged along the second direction such that an occupancyrate of the cylindrical lenses with respect to the second direction ishigher in an area closer to the light entering surface and lower in anarea farther from the light entering surface; and flat portions formedon the other one of the light exiting surface and the opposite platesurface of the light guide plate, the flat portions being flat along thefirst direction and the second direction, the flat portions beingarranged adjacent to the cylindrical lenses with respect to the seconddirection such that an occupancy rate of the flat portions with respectto the second direction is lower in the area closer to the lightentering surface and higher in the area farther from the light enteringsurface, the flat portions having an occupancy rate of 0% with respectto the second direction on a light entering surface side.
 2. Thelighting device according to claim 1, wherein the exiting lightreflecting portion and the prism portion are formed on the oppositeplate surface side of the light guide plate, and the lenticular lensportion is formed on the light exiting surface side of the light guideplate.
 3. The lighting device according to claim 1, further comprising areflecting member including a reflecting surface for reflecting light,the reflecting member being disposed opposite the opposite plate surfaceof the light guide plate, wherein the exiting light reflecting portionand the prism portion are formed on the light exiting surface side ofthe light guide plate, and the lenticular lens portion is formed on theopposite plate surface side of the light guide plate.
 4. The lightingdevice according to claim 1, wherein each of the cylindrical lenses ofthe lenticular lens portion has a concave shape.
 5. The lighting deviceaccording to claim 1, wherein each of the cylindrical lenses of thelenticular lens portion has a convex shape.
 6. The lighting deviceaccording to claim 5, wherein the cylindrical lenses have heights fromthe light exiting surface gradually and continuously decreasing as adistance from the light entering surface with respect to the firstdirection increases.
 7. The lighting device according to claim 5,wherein the exiting light reflecting portion and the prism portion areformed on the opposite plate surface side of the light guide plate, thelenticular lens portion is formed on the light exiting surface side ofthe light guide plate, the cylindrical lenses of the lenticular lensportion include a first cylindrical lens having a smaller height and asecond cylindrical lens having a larger height, and a clearance isprovided between the first cylindrical lens and the light exiting-sideanisotropic light collecting portion.
 8. The lighting device accordingto claim 1, wherein the lenticular lens portion and the flat portionsare formed such that the occupancy rate of the cylindrical lenses withrespect to the second direction gradually and continuously decreases asa distance from the light entering surface with respect to the firstdirection increases and the occupancy rate of the flat portions withrespect to the second direction gradually and continuously increases asthe distance from the light entering surface with respect to the firstdirection increases.